Digitized  by  the  Internet  Arciiive 

in  2008  with  funding  from 

IVIicrosoft  Corporation 


http://www.archive.org/details/fieldfortificatiOOwheerich 


FIELD  FORTIFICATIONS,  ETC.: 


A  TEXT-BOOK 


FOR  THE  USE  OP  THE 


CADETS  OF   THE   UNITED   STATES   MILITARY  ACADEMY 


WEST   POINT,   ¥.   y. 


BY 

J.    B.    WHEELER, 

PROFESSOR  OF  CIVIL  AND   MILITARY   ENGINEEIIING    IN  THE   MILITARY  ACADEMY 
AT  WEST  POINT,  N.   Y.,   AND  BREVET   COLONEL,   UNITED   STATES  ARMY. 


NEW   YORK ; 

D.    VAN    NOSTEAND. 

1880. 


CorYKMiHT.    18S0.    1>.    VAN  NOSTRAND. 


"  There  are  five  tilings  from  which  the  soldier  must 
never  he  separated :  his  gun,  his  ammunition,  his 
knapsack,  his  rations  for  four  days,  and  an  in- 
trenching  tool.' 

Napoleon. 


PREFACE. 


This  text-book  is  prepared  for  the  use  of  the 
cadets  of  the  United  States  Military  Academy  while 
pursuing  their  course  of  studies  in  the  subject  of 
'^military  engineering." 

The  endeavor  has  been  made  to  state  concisely 
and  plainly  the  principles  upon  which  the  "art  of 
fortification"  is  based,  and  to  give  all  information 
likely  to  be  of  practical  use  to  a  young  officer  while 
serving  in  the  field.  All  unnecessary  details  have 
been  avoided,  leaving  explanations  and  illustrations 
of  that  kind  to  be  introduced  into  the  class-room. 

The  elementary  form  of  the  work  and  the  method 
of  treatment  of  the  subject  are  based  upon  the  as- 
sumption that  the  readers  of  the  book  are  beginners 
and  know  nothing  of  the  principles  of  fortification. 

West  Point,  N.  Y..  February,  1880. 


\  B  T^  A  R  ' 

Y  OF  THF 

UNIVERSITY 

CONTENTS. 

CHAPTER   I. 

General  Principles  and  Definitions. 

Article.  Page 

1.  Definition  of  the  term,  position 7 

2.  Strong  positions 8 

3.  Fortifications,  their  object 8 

4.  Classes  of  fortifications 9 

5.  Field  fortifications   10 

6.  Kinds  of  field  fortifications 10 

7.  General  principles  to  be  observed  in  the  construction  of 
fortifications 11 

8.  General  methods  followed  to  fulfil  these  conditions  ....  12 

9.  Active  and  passive  defence  of  a  fortification 12 

10.  Definition  of  the  term,  ditch 13 

11.  The  site  of  a  work 14 

12.  The  meaning  of  the  term,  intrenched  position 14 

CHAPTER    II. 

Elements  of  the  Profile  of  a  Fortification. 

13.  The  parapet 15 

14.  The  terreplein 15 

15.  The  profile 15 

16.  The  berm 18 

17.  The  ditch 18 

18.  The  foot  of  a  slope,  the  crest,  etc 18 

19.  The  principal  lines  of  the  profile. 19 


Tl  CONTENTS. 

CHAPTER    III. 

Dimensions  and  Inclinations  given  to  the  Ijines  and  Slopes 
of  a  Parapet. 

ARTICLE.  PAGE 

20.  Height  that  a  parapet  should  have 21 

21.  Definition  of  the  terms,  command  and  relief 22 

22.  Thickness  that  a  parapet  should  have 23 

23.  Width  and  height  of  banquette 24 

24.  Inclination  given  to  the  interior  slope 25 

25.  Inclination  given  to  the  superior  slope 27 

26.  Inclination  of  the  exterior  slope 28 

27.  Width  and  uses  of  a  berm 28 

28.  The  uses,  and  the  dimensions  of  a  ditch 29 

29.  Slope  of  scarp  and  counterscarp 30 

30.  Method  of  determining  the  dimensions  to  give  the  ditch  30 

31.  Method  used  in  practice 32 

32.  The  normal  profile  of  a  field  fortification 33 

CHAPTER    IV. 
The  Trace  of  a  Field  Fortification. 

33.  Definition  of  the  terms,  trace  and  sub-crest 34 

34.  The  kinds  of  fire  to  which  a  fortification,  or  a  body  of 
troops  may  be  exposed 34 

35.  The  salient  and  re-entering  angles  of  a  trace 36 

36.  The  general  principles  to  be  observed  in  the  selection 

of  a  trace 36 

37.  The  reasons  for  observing  these  principles 37 

CHAPTER    V. 
Field  Works. 

38.  Classification  of  field  fortifications  into  field  works  and 
lines 39 

39.  Classes  of  field  works 39 


CONTENTS.  Vii 

ARTICLE.  PAGE 

40.  Open,  and  half-closed  field  works 41 

41.  Lunettes 42 

42.  Bastioned  front 42 

43.  Closed  field  works 43 

44.  Redoubts 43 

45.  Star  redoubts  44 

46.  Bastioned  forts 45 

47.  Nomenclature  of  the  bastioned  fort 46 

•  48.  Sectors  without  fire,  and  dead  spaces 47 

49.  Flanked  dispositions 48 

50.  Relations  existing  between  the  different  parts  of  a  bas- 
tioned front 49 

51.  The   least  and  the  greatest  exterior  sides  that  can  be 
used  in  bastioned  fronts 51 

52.  Defects  to  be  found  in  a  bastioned  fort 52 

53.  Defects  of  star  forts 53 

CHAPTER  VI. 

Lines. 

54.  Different  classes  of  lines 54 

55.  What  is  meant  by  a  continued  line 54 

56.  What  is  meant  by  a  line  with  intervals 54 

Continued  Lines. 

57.  Different  kinds  of  continued  lines 55 

58.  Tenaille  line , .55 

59.  Redan  line 57 

60.  Indented  lines 57 

61.  Bastioned  lines 58 

62.  Advantages  and  disadvantages  of  continued  lines 58 

Lines  with  Intervals. 

63.  The  positions  occupied  by  the  field  works  forming  a  line 
with  intervals 59 

64.  Third  line 61 

65.  The  advantages  and  defects  of  lines  with  intervals  com- 
pared with  other  kinds  of  lines 62 


Vlll  CONTENTS. 

CHAPTER   VII. 

The  size  of  a  Field  Work,  the  number  of  its  Garrison,  and 
the  Selection  of  its  Trace. 

ARTICLE.  PAGE 

66.  The  size  to  give  to  a  field  work. 64 

67.  The  number  of  the  garrison  to  defend  a  field  work .     65 

68.  The  amount  of  space  to  be  enclosed 66 

69.  The  relation  between  the  space,  and  the  length  of  inte- 
.     rior  crest  of  a  square  redoubt  when  the  number  of  the 

garrison  is  known 67 

70.  The  things  to  be  observed  in  the  selection  of  trace 69 


CHAPTER    VIII. 

Construction  of  Field  Works. 

71.  The  operation  known  as  ''  tracing  " 72 

72*  The  operation  known  as  "  profiling  " 73 

73.  The  method  employed  to  construct  the  parapet 76 

74.  The  time  which  is  required  to  build  a  field  work 78 

CHAPTER    IX. 
Revetments. 

75.  What  is  meant  by  the  term,  revetment 81 

76.  Kinds  of  materials  used  for  revetments 81 

77.  Fascines,  and  their  construction. 82 

78.  Fascine  revetments 83 

79.  Gabions,  and  their  construction 85 

80.  Hurdle  revetments 87 

81.  Revetments  of  timber 87 

82.  Revetments  made  of  planks 89 

83.  Revetments  made  with  casks,  barrels,  etc 90 

84.  Sand-bags,  and  their  use  in  revetments 90 

85.  Sod  revetments,  and  their  construction 92 

86.  Pisa  revetment,  and  its  construction 93 

87.  Revetments  of  other  kinds. 94 


CONTENTS,  IX 

CHAPTER   X. 
Defilade. 

ARTICLE.  PAGE 

88.  What  is  meant  by  defilade,  and  how  a  field  work  may- 
be defiladed 96 

89.  Plane  of  defilade,  and  its  use 97 

90.  The  amount  of  area  to  be  defiladed 98 

91.  The  method  used  to  obtain  the  position  of  the  plane  of 
defilade 99 

93.  Front  and  reverse  defilade 102 

94.  Methods  used  to  defilade  a  work  from  reverse  fires 104 

95.  The  method  used  to  determine  the  position  of  the  plane 

of  reverse  defilade 106 

96.  The  method  of  defilade  by  means  of  traverses 108 

97.  Defilade  of  a  line. .   : 110 

CHAPTER    XI. 
The  Interior  Arrangements  made  in  a  Field  Work. 

98.  Classes  of  interior  arrangements 114 

Arrangement  of  the  Parapet. 

99.  Arrangement  of  the  parapet  for  defence 115 

100.  Barbette  fire  of  artillery 115 

101.  Method  of  constructing  the  trace  of  a  barbette 116 

102.  Pan-coupe,  when  used 118 

103.  Embrasure  fire  of  artillery 120 

104.  Method  of  constructing  the  trace  of  an  embrasure 121 

105.  Direct  and  oblique  embrasures 124 

106.  Comparative  advantages  and  defects  pertaining  to  bar- 
bette and  embrasure  fires , 125 

107.  Bonnettes,  and  their  uses 125 

108.  Loop-holes,  and  their  object  . « , 126 

109.  Traverses,  their  kind  and  their  construction 128 

110.  Construction  of  splinter-proof  traverses 130 

111.  Platforms  for  artillery  in  field  works 132 


X  CONTENTS. 

Arrangements  for  Sheltering  the  Troops,  etc.  from  the  effects 
of  the  Enemy's  Fire. 

ARTICLE,  PAGE 

112.  Bomb-proofs  and  splinter-proofs  for  the  use  of  the  gar- 
rison     135 

113.  Method  of  constructing  bomb-proofs 136 

114.  Blindages 138 

1 15.  Construction  of  splinter-proofs 138 

116.  Powder  magazines 139 

117.  Service  magazines,  their  construction 141 

118.  Gun-shelters 143 

119.  Materials  used  in  construction  of  shelters 143 

120.  Example  of  a  bomb  proof  used  in  the  field  works  sur- 
rounding the  city  of  Washington  in  1861-5 144 

121.  Example  of  a  powder  magazine  used  in  the  same  works  145 

122.  The  position  to  be  given  to  shelters  of  this  class  in  a 
field  work 146 

Arrangements  affording  Communications,  etc. 

123.  Passages  leading  into  a  field  work,  and  where  placed. . .   148 

124.  The  method  used  to  conceal  the  interior  of  the  work 
from  being  seen  through  the  opening  in  the  parapet . . .   148 

126.  Barriers,  to  close  the  passages 151 

127.  Bridges  to  cross  the  ditch 153 

128.  Ramps,  their  uses  and  dimensions 154 

Arrangements  for  the  Comfort  and  Health  of  the  Garrison. 

129.  Nature  of  the  arrangements  to  be  made 155 

Other  Interior  Arrangements  used. 

130.  Arrangements  of  a  secondary  kind 156 

131.  Block-houses,  their  dimensions  and  uses 157 

132.  Isolated  block-houses 160 

133.  Stockades 161 

CHAPTER  XII. 

Arrangements  made  Exterior  to  the  Parapet. 

134.  Different  kinds  used  exterior  to  a  parapet 166 


CONTENTS.  XI 

ARTICLE.  PAGE 

Ditch  Defences. 

135.  Classes  of  defences  used  in  the  ditch 166 

136.  Caponnieres 167 

137.  Scarp  and  counter-scarp  galleries 168 

Obstacles. 

138.  Two  classes  of  obstacles 170 

139.  The  ditches  as  obstacles 170 

140.  Abatis 172 

141.  Entanglements 173 

142.  Che vaux-de-f rise 173 

143.  Palisading. 174 

144.  Fraises 175 

145.  Small  pickets 175 

146.  Crow's  feet,  iron  harrows 176 

147.  Military  pits,  deep  and  shallow 176 

148.  Slashing  of  timber 177 

149.  Torpedoes 178 

150.  Stone-fougasses 179 

151.  Shell-fougasses 181 

152.  Inundations 181 

153.  General  uses  of  military  obstacles 182 

CHAPTER    XIII. 

Application  of  Field  Fortifications  to   Sites   upon  Irregular 
Ground. 

154.  The  general  considerations  of  the  case 184 

155.  Three  cases 185 

156.  Modification  of  profile  caused 185 

157.  Modification  of  the  trace 188 

158.  Defence  of  steep  slopes 190 

159.  Defence  of  precipitous  slopes 191 

160.  General  plan  of  defence  influences  the  engineer  in  the 
selection  of  the  kind  of  works  and  the  arrangement  of 
these  works  to  defend  a  position 191 


Xn  CONTENTS. 

Bridge  Heads. 

ARTICLE.  PAGE 

161.  Bridge-head,  its  meaning 192 

162.  The  object  to  be  attained  by  the  use  of  a  bridge-head. .  193 

163.  Strong  bridge-heads,  their  use  195 

164.  Bridge-heads  called  horn  works,  crown  works,  etc 197 


CHAPTER    XIV. 
Hasty  Intrenchments. 

165.  Hasty  defences , 200 

166.  Shelter-trenches,  or  rifle-pits 200 

167.  Construction  of  shelter-trenches 201 

171.  Use  of  shelter-trenches  as  covered  communications 203 

172.  Trace  of  a  shelter  trench 205 

173.  Shelters  for  artillery  or  cavalry 206 

174.  Defence  of  a  house  207 

175.  Tambours 208 

176.  Machicoulis  galleries 210 

177.  Expedients  similar  in  principle  to  a  machicoulis  gallery  210 

178.  Use  of  stone  walls,  hedges,  etc.,  in  defence 211 

179.  The  defence  of  woods 211 

180.  The  preservation  and  destruction  of  roads 213 

181.  Intrenched  field  of  battle  and  example 213 

CHAPTER    XV. 
Attack  and  Defence  of  Field  Fortifications. 

182.  The  attack,  when  an  assault,  when  a  siege ;    221 

183.  Open  assault,  three  periods  of 222 

184.  Preliminary  operations  and  the  artillery  attack 222 

185.  The  operations  of  the  second  period 224 

186.  The  operations  of  the  third  period 224 

187.  Attack  by  surprise 225 

188.  Unexpectedness  of  attack  important  to  success 226 


CONTENTS.  Xlll 

ARTICLE.  PAGE 

189.  Attack  made  by  artillery  only 226 

190.  Key  point  of  position  to  be  selected  to  attack 226 

191.  Defence  of  a  field  fortification 226 

192.  Memoranda  furnished  the  commanding  officers  of  the 
field  works  surrounding  the  city  of  Washington  relative 

to  the  defence 227 

193.  Examples  of  attack  and  defence  of  field  fortification. . . .   237 

194.  The  conclusion  to  be  drawn  from  the  history  of  assaults 
upon  field  works  in  recent  wars \ 239 


INTRODUCTION. 


Iktrenchmekts  are  co-eval  with  man.  In  all  ages 
they  have  played  important  parts  in  the  contests  carried 
on  by  force,  when  men  have  striven  for  the  mastery. 

They  have  been  recognized  by  the  great  masters  of 
the  art  of  war  as  important  adjuncts  of  their  military 
operations,  and  have  been  freely  used  by  them  in  their 
campaigns. 

Napoleon  said,  ^' those  who  proscribe  the  help  which 
the  engineer's  art  may  afford  in  the  field,  deprive  them- 
selves voluntarily  of  an  auxiliary  force  and  expedient, 
never  hurtful,  always  useful,  and  often  indispensable." 

Frederick  the  Great,  in  his  Memoires,  says, — '*  Offi- 
cers require  different  kinds  of  knowledge,  but  one  of 
the  principal  is  that  of  fortification." 

General  Sherman  says  in  his  memoirs,  '^  earth- 
forts,  especially  field-works,  will  hereafter  play  an  im- 
portant part  in  wars,  because  they  enable  a  minor  force 
to  hold  a  superior  one  in  check  for  a  time,  and  time 
is  a  most  valuable  element  in  all  wars." 

The  general  of  modern  times  who  first  prominently 
recognized  the  great  merit  of  field  works,  and  who  saw 


2  INTRODUCTION. 

in  them  ^^an  auxiliary  force,"  was  the  emperor,  Charles 
V.  of  Germany. 

To  each  regiment  of  infantry  he  attached  a  body  of 
pioneers,  numbering  four  hundred,  under  the  command 
of  a  special  officer,  and  provided  them  with  intrenching 
tools.  These  men  were  used  to  construct  fortifications, 
and  perform  the  duties  of  engineer  soldiers. 

The  use  of  this  kind  of  force  was  fully  appreciated 
by  him,  and  on  more  than  one  occasion  proved  of  great 
service  to  him. 

It  is  mentioned,  that  in  1547,  the  emperor  found 
himself  in  the  presence  of  the  enemy,  who  were  twice 
his  strength  in  numbers,  but  who  made  the  mistake  of 
not  attacking  at  once.  Charles  V.  immediately  began 
to  intrench  his  army,  and,  by  morning  of  the  following 
day,  was  capable  of  repulsing  the  enemy.  He  continued 
to  strengthen  his  position  for  twelve  days.  On  the 
thirteenth  day,  he  received  re-inforcements  and  moved 
against  the  enemy. 

It  is  stated,  that  Peter  the  Great,  at  the  battle  of 
Pultowa,  which  terminated  in  the  total  defeat  of  the 
Swedish  army,  owed  his  success  to  intrenchments 
which  he  had.  had  the  foresight  to  construct  in  front 
of  his  line  of  battle,  upon  the  night  before  the  action. 

The  simple  redoubt  in  the  pass  near  Montenotte, 
defended  by  Colonel  Kampon,  in  1796,  enabled  Bona- 
parte to  execute  the  details  of  a  campaign  unparalleled 
in  the  records  of  military  history.     Relative  to  this  re 


L\TR  OD  UCTIOX.  3 

doubt  and  its  defence,  Thiers  says,  "^  It  saved  the  gen- 
eral's plans,  and  perhaps,  the  future  of  the  campaign." 

Intrench ments  played  an  important  part  in  the  late 
war  in  the  United  States. 

In  the  beginning  of  this  war,  (1861),  the  sentiment 
or  general  opinion  of  the  American  volunteers  was 
adverse  to  intrenchments.  The  manual  labor  requisite 
for  the  construction  of  intrenchments  was  regarded  by 
them  as  degrading;  their  idea  was  ^*a  fair  stand-up 
fight,"  in  the  open  field.  They  applied  the  term 
*^ dirt-diggers"  to  the  advocates  of  intrenchments,  and 
considered  '^masked  batteries"  as  devices  unbecoming 
a  civilized  people. 

Experience  in  war,  and  great  necessity  soon  drove 
such  erroneous  views  from  their  minds,  and  before 
the  war  ended,  these  same  soldiers  threw  up  intrench- 
ments whenever  the  army  halted,  of  their  own  free 
will  and  accord. 

A  writer  stated,  on  this  subject,  that  ^'they  waited 
neither  for  orders,  nor  deployment  of  skirmishers,  nor 
formation  of  lines.  *  *  *  *  The  rule  was  that  the 
troops  should  proceed  with  this  work  without  wait- 
ing for  orders." 

Their  good  sense  soon  caused  them  to  appreciate 
the  value  of  both  natural  and  artificial  aids  in  the  de- 
fence, and  to  learn  that  the  fate  of  a  battle  frequently 
depended  upon  some  slight  protection  given  to  a  line, 
a  protection  so  slight  in   many  cases  as  to   be  hardly 


4  INTRODUCTION. 

worthy  of  the  name,  such  as  a  few  rails  heaped  to- 
gether, a  shallow  trench,  etc.  The  result  was  that 
the  American  soldier  became  an  adept  in  intrench- 
ing himself   on  the  field  of  battle. 

The  Confederates  made  great  use  of  intrenchments, 
and  by  their  aid  inflicted  great  losses  upon  our  troops. 

General  Grant  crossed  the  Rapidan  in  May,  1864,  and 
attacked  the  enemy  in  the  Wilderness.  His  most 
desperate  assaults  were  not  successful  in  driving  the 
confederates  from  their  intrenchments.  He  was  suc- 
cessful only  by  moving  around  the  position. 

The  losses  suffered  by  the  Union  army,  under 
General  Grant  from  the  time  he  crossed  the  Rapidan 
until  he  reached  the  James  river, — about  one  month, 
— were  equal  in  numbers  to  the  entire  force  op- 
posed to  him  in  the  beginning,  when  he  crossed  the 
Rapidan  ;  and  these  losses  were  largely  due  to  the  fact 
that  the  confederates  occupied  *'  intrenched  "  positions. 

General  Sherman  bears  testimony  in  many  places 
to  the  influence  of  intrenchments.  In  speaking  of 
the  assaults  made  on  the  enemy's  lines,  at  Kenesaw 
mountain,  June  24,  1864,  he  says.  '^The  two  assaults 
were  made  at  the  time  and  in  the  manner  prescribed, 
and  both  failed,  costing  us  many  valuable  lives,  *  *  *  * 
our  aggregate  loss  being  near  three  thousand  men, 
while  we  inflicted  little  loss  upon  the  enemy  who 
lay  behind  his  well  formed  breast- works.'' 

Tiie  experience  acquired  in  this  war  in  the  United 


IXTRODUCTION.  0 

States  proved  the  necessity  and  value  of  intrencb- 
ments,  even  when  extemporized  and  constructed  in  the 
presence  of  an  enemy.  It  also  proved  that  a  very  slight 
intrenchment,  when  manned,  and  with  the  approaches 
to  it  swept  by  artillery,  was  practically  impregnable. 

The  cost  of  carrying  a  line  of  intrenchment  is 
incidentally  mentioned  in  one  of  the  reports  of  Major 
General  H.  G.  AVright,  commanding  the  Sixth  corps 
of  the  army  of  the  Potomac,  in  the  attack  upon  Peters- 
burg, in  April,  1865,  and  now  the  Chief  of  Engi- 
neers, United  States  Army.  He  says,  it  '^cost  us,  in 
killed  and  wounded,  a  number  equal  perhaps  to  that  of 
the  entire  force  of  the  enemy  actually  opposed  to  us. 
It  was  an  attack  of  nearly  two  divisions  against  a 
picket  line  covered  by  a  simple  trench  and  parapet ;  but 
had  it  been  held  by  two  ranks  of  good  troops  it  is 
doubtful  if  it  could  have  been  carried  even  by  an  entire 
corps."  His  conclusion  was  that  **a  well  intrenched 
line,  defended  by  two  ranks  of  infantry  cannot  be  car- 
ried by  a  direct  attack,"  unless  there  are  favorable  cir- 
cumstances, which  it  is  not  necessary  to  mention  here. 

The  recent  war  between  Russia  and  Turkey  confirms 
the  experience  gained  by  us  in  our  late  war,  and 
places  the  intrenching  tool  almost  on  a  level  with  the 
musket. 

Lieut.  Greene  in  his  report  says,  that  General 
Skobeleff  made  his  men  carry  the  spades  and  shovels 
on  their  persons.     lie  remarks,  relative  to  this  intrench- 


6  INTRODVCTIOX. 

ing  tool,  ^'they  were  heavy  (weighing  over  five 
pounds),  they  were  uncomfortable,  they  were  in  every 
way  inconvenient,  but  each  man  had  learned  by  hard 
experience  to  feel  that  his  individual  life  depended 
upon  his  musket  and  his  spade — and  he  took  good  care 
to  lose  neither  the  one  nor  the  other.'' 

The  student,  seeing  the  advantages  accruing  from 
intrenchments  hastily  const];ucted,  can  easily  draw  his 
conclusions  as  to  the  value  of  lines  of  fortifications 
when  there  is  time  to  build  them  properly. 

The  famous  lines  of  Torres  Vedras,  in  Portugal 
constructed  by  Lord  Wellington;  the  line  of  works 
built  around  the  city  of  Washington  during  the  late 
war ;  the  line  of  works  defending  Nashville,  Ten- 
nessee ;  and  others  are  interesting  subjects  of  study, 
and  show  how  a  defeated,  or  an  inferior  army  by  their 
use  is  able  to  hold  its  ground,  for  more  or  less  time, 
against  a  superior  or  victorious  enemy. 

Field  fortifications  have  attained  such  great  im- 
portance, owing  to  the  long  range,  the  precision,  and 
the  rapid  fire  of  modern  arms,  that  no  soldier  can  afford 
to  be  without  a  knowledge  of  the  great  principles  un- 
derlying this  branch  of  military  engineering.  The  re- 
mark of  Frederick  the  Great,  true  in  his  day,  is  still 
true  at  the  present  time,  viz:  '^Officers  require  differ- 
ent kinds  of  knowledge,  but  one  of  the  principal  is 
that  of  fortification." 


FIELD    FORTIFICATIONS. 


CHAPTEE    I. 

GE!!fERAL   PRINCIPLES   AND   DEFINITIONS. 

1.  Positions. — The  term,  position,  is  applied 
by  military  writers  to  any  piece  of  ground  which  is,  or 
may  be,  occupied  by  a  body  of  troops  for  the  purpose 
either  of  making  or  repelling  an  attack. 

When  the  purpose  is  that  of  repelling  an  attack, 
the  position  is  called  a  defensive  one.  The  motives 
which  lead  a  body  of  troops  to  occupy  a  defensive  posi- 
tion may  spring  from  several  causes.  The  most  pro- 
minent of  these  causes  are  smallness  of  numbers,  in- 
feriority in  arms,  lack  of  experience  in  war,  or  similar 
differences,  which,  at  the  time,  render  the  enemy 
superior  in  strength. 

A  defensive  position  is  occupied  principally  for 
the  purpose  of  neutralizing  this  temporary  superiority 
of  o-n  enemy,  and  to  give  to  the  troops  holding  the 
position,  the  chances  of  making  a  successful  resistance 
to  any  attack  made  to  dislodge  them. 


8  FIELD   FORTY  FIG  ATI  ONS. 

2.  Strong  positions. — Positions  are  called  strong, 
when  they  give  to  their  defenders  all  the  chances  of 
making  a  successful  resistance  against  any  sudden  as- 
sault which  may  be  made  by  an  enemy. 

When  the  natural  features  of  a  position  are  such, 
that  the  defenders  can  shelter  themselves  from  the 
enemy's  fire,  and  at  the  same  time  be  free  to  pour  a 
fire  upon  the  enemy's  columns  as  they  approach,  it  is 
evident  that  the  chances  arc  decidedly  in  favor  of  a 
successful  resistance  by  the  defence,  and  the  position 
is  more  or  less  a  strong  one.  Positions  are  not  equally 
strong,  in  consequence  of  the  natural  features  of  the 
ground  in  one  case  being  less  favorably  disposed  for 
shelter,  than  in  another.  Their  strength  may  however 
be  increased  by  artificial  means,  and  so  much  so,  in 
many  cases,  as  to  render  them  technically  "  strong  "  or 
impregnable. 

3.  Fortifications. — The  artificial  means  used  to 
give  additional  strength  to  a  position  are  termed 
fortifications,  from  the  verb,  "to  fortify''  Yfor- 
its,  strong,  and  facere  to  make]  derived  from  the 
Latin. 

The  skilful  combination  of  these  means,  and  their 
construction,  constitute  a  branch  of  Military  Engineer- 
ing known  as  the  ''Art  of  fortification." 

The  object  of  the  art  of  fortification  is  to  locate 
and  construct,  upon  positions  selected  for  defence,  such 
additional    aids   or   helps,  that   the   defenders   can    by 


GENERAL   PRINCIPLES  AND   DEFINITIONS.  9 

their  use  remove  partially,  if  not  entirely,  the  dis- 
parity existing  between  them  and  their  assailants. 

The  art  of  fortification  may  therefore  be  defined  to 
be  that  branch  of  military  engineering  which  has  for  its 
object  the  strengthening  of  positions  selected 
for  defence. 

4.  Classes  of  fortifications. — Fortifications  are 
usually   divided  into  two  general  classes,   viz.  : 

Permanent  and  Temporary. 

That  class  of  fortifications  which  is  usually  con- 
structed in  tim'es  of  peace  for  the  purpose  of  strength- 
ening positions  which  may  be  of  military  importance  in 
case  of  a  future  war,  is  termed  permanent.  Fortifica- 
tions of  this  class  are  built  usually  with  great  care,  and 
of  durable  materials.  They  are  expected  to  last  for  a 
considerable  time,  and  are  therefore  comparatively  per- 
manent in  their  nature. 

That  class  of  fortifications  which  is  usually  built 
after  war  has  been  declared,  and  to  strengthen  posi- 
tions which  have  suddenly  acquired  a  military  import- 
ance, is  known  as  temporary.  Fortifications  of  this 
class  may  in  some  cases  become  permanent,  but  ordi- 
narily they  are  built  in  a  comparatively  short  time,  of 
materials  which  are  near  at  hand  and  can  be  obtained 
quickly,  and  frequently  by  the  labor  of  the  troops. 
The  positions  strengthened  by  them  are  frequently  of 
transitory  importance   and    soon   abandoned,    and   the 


10  FIELD   FORTIFICATIONS. 

materials  used  are  oftentimes  perishable  in  their 
nature.  The  fortifications  are  in  use,  in  many  cases, 
but  for  a  short  time  ;  are  wanting  in  durability  ;  and 
are  therefore  temporary  in  their  nature. 

5.  Field  fortifications. — The  temporary  fortifi- 
cations constructed  by  the  labor  of  the  troops  constitute 
the  greater  part  of  the  fortifications  of  this  class.  The 
troops  are  said  to  be**  in  the  field  "  at  this  time,  and 
the  fortifications  constructed  by  them  are  usually  known 
as  field  fortifications. 

The  subject  of  this  book  is  a  general  discussion  of 
the  principles  used,  and  the  kind  of  works  employed,  in 
fortifying  a  position  in  the  field,  by  the  labor  of  troops. 

6.  Kinds  of  field  fortifications. — Fortifica- 
tions constructed  in  the  field  are  of  two  general  kinds, 
according  to  the  time  employed  in  their  construction, 
viz  :  Hasty  and  Ordinary. 

Hasty  fortifications  are  those  which  must  be  built 
in  the  time  intervening  between  the  end  of  a  march 
and  the  beginning  of  a  battle.  This  time  is  a  very  few 
hours  at  most,  and  the  fortifications  must  be  finished 
usually  in  a  single  night,  or  they  will  be  useless. 

Ordinary  fortifications  are  also  constructed  hur- 
riedly,  but  there  is  time  enough  to  practically  finish 
them  according  to  the  plans  upon  which  they  are 
laid  out. 

Hasty  fortifications  are  the  kind  built,  in  many 
cases,   in  the   actual  presence  of  an  enemy  ;  ordinary 


GENERAL    FltlXCIFLES  AND   DEFINITIONS,  11 

fortifications  are  those- built  before  the  enemy  arrives 
upon  the  ground. 

7.    General  principles    of    fortifications. — 

Fortifications,   whatever  be  their  class,  are  merely  pas- 
sive means  of  defence. 

Certain  general  conditions  must  be  satisfied  by  a 
defensive  position,  to  enable  an  armed  force  occupying 
it  to  contend  successfully  against  an  assailant,  superior 
either  in  numbers,  discipline,  or  arms.  These  condi- 
tions must  be  favorable  to  the  defence  and  unfavorable 
to  the  assailant ;  and  when  they  do  not  exist  naturally  in 
the  position,  must  be  supplied  by  means  of  fortifications. 
These  conditions  for  a  position,  and  in  consequence,  for 
a  fortification,  may  be  briefly  enumerated  to  be  as  follows: 

1.  A  shelter  must  be  provided  to  protect  the  defend- 
ers against  the  missiles  of  the  assailant,  and  to^&eoHXe 
them  from  his  view. 

2.  The  position  should  be  so  arranged  that  an  as- 
sailant can  not  approach  within  cannon  range  and 
not  be  exposed  to  the  fire  of  the- defence. 

3.  If  practicable,  the  position  should  be  taken, 
and  the  shelter  arranged,  so  that  an  approach  of  the 
enemy  would  be  difficult,  and  the  enemy's  movements 
towards  the  position  be  greatly  impeded. 

4.  The  position  and  shelter  should  be  arranged  so 
that  the  defenders  movements  to  defend  the  position 
should   not  be  hindered  or  impeded  in  any  way. 

8.   General     method    of  complying    with 


12  FIELD   FORTIFICATTOM S. 

these  conditions. — The  first  conditioPx  or  principle 
named  is  usually  satisfied  by  making  an  excavation, 
and  heaping  the  mass  of  earth  thus  obtained,  until 
it  is  high  enough  and  thick  enough  to  screen  and 
protect  the  defenders. 

The  second  is  fulfilled  ordinarily  by  clearing  away 
the  ground  in  front  of  the  position,  and  within  cannon 
range,  of  all  trees,  houses,  enclosures,  hedges,  etc., 
which  might  be  used  by  the  enemy  as  a  screen  ;  and 
by  arranging  the  mass  of  earth  used  as  a  shelter,  so 
that  the  defenders  can  fire  over  it,  or  through  it,  and 
sweep,  with  their  fire,the  ground  over  which  the  enemy 
must  approach. 

The  third  :s  observed  by  placing  the  fortification 
behind  some  natural  obstruction,  as  a  marsh,  a  water- 
course, etc.  If  this  is  not  practicable,  it  is  fulfilled 
by  placing  obstacles  in  front  of  the  fortification  and 
arranging  them  so  that  they  shall  impede  the  assail- 
ant's approach,  but  not  screen  his  movements,  nor 
protect  him  from  the  fire  of  the  defence. 

The  fourth  is  complied  with"  by  removing  any  ob- 
structions which  might  be  in  the  way  of  the  free 
movements  of  the  defence,  and  by  making  communi- 
cations which  can  be  used  by  the  defenders  in  moving 
from  one  part  of  the  position  to  another. 

9.  Active  and  passive  defence. — The  terms, 
active  and  passive,  are  used  to  designate  the  kind 
of  resistance  which  is  offered  in  the  defence  of  a  posi- 


GENERAL   PRINCIPLES  AND  DEFINITIONS.  13 

tion.  If  the  defenders,  seeing  an  opportune  moment, 
should  leave  the  position  and  attack  the  enemy  without 
waiting  to  be  attacked  ;  or  if  during  the  assault, 
they  leave  the  position  for  the  same  purpose,  the  re- 
sistance made  is  termed  an  active  defence. 

If  no  attempt  is  made  to  leave  the  work  to  attack  the 
enemy,  the  resistance  offered  is  known  as  a  passive 
defence. 

An  active  defence  can  be  made,  as  a  rule,  only  by 
a  force  which  is  strong  enough  and  numerous  enough 
to  leave  the  position  and  become  an  attacking  force. 
A  passive  defence  is  usually  the  resort  of  a  force 
which  is  decidedly  inferior  to  the  assailant  ;  or  is  the 
defence  made  when  the  object  of  the  resistance  is  fully 
attained  if  the  enemy  fails  in  his  assault. 

An  active  defence  requires  that  the  third  principle 
just  mentioned  should  be  modified.  It  requires  that 
the  arrangements,  organized  to  impede  an  enemy's 
approach,  should  be  made  so  as  not  to  interfere  with 
the  free  movements  of  the  defenders. 

10.  DefinitionSo — The  principal  parts  obtained 
in  the  construction  of  an  earthern  shelter  are  the 
mass  of  earth  which  is  heaped  ujd,  and  the  excavation 
from  w^iich  it  was  taken. 

When  the  excavation  is  between  the  mass  of  earth 
and  the  enemy,  it  is  called  a  ditch  ;  if  the  mass  of 
earth  is  between  the  excavation  and  the  enemy,  the 
excavation  is  then  designated  as  a  trench. 


Itt  FIELD   FORTIFICATIONS. 

It  will  be  seen  that  the  trench  is  the  simplest 
form  of  shelter,  and  the  most  quickly  made.  It  fails 
to  fully  satisfy  the  conditions  just  named,  as  will  be 
hereafter  shown. 

11.  The  ground  occupied  by  a  fortification  is  called 
the  site  of  the  work  ;  and  a  plane  tangent  to  this 
ground  is  called  the  plane  of  site. 

The  outline  of  a  fortification  as  drawn  upon 
the  ground,  or  its  projection  upon  a  horizontal  plane, 
is  termed  the  trace.  A  section  of  the  fortification 
made  by  a  vertical  plane  passed  perpendicularly  to  the 
principal  or  directing  line  of  the  trace,  is  called  the 
profile. 

12.  Any  position  strengthened  by  fortifications 
made  of  earth  is  said  to  be  intrenched  ;  the  fortifica- 
tions used  for  the  purpose  are  termed  intrench- 
nxents.  This  latter  term  is  usually  applied  to  works 
of  considerable  extent  which  are  used  to  shelter  large 
bodies  of  men. 


CHAPTER    II. 

ELEMENTS   OF  THE   ORDHsTARY   PROFILE. 

13.  Parapet. — Different  names  are  used  to  desig- 
nate the  mass  of  earth  employed  for  shelter,  according 
to  the  ohject  it  serves. 

When  this  mass  is  arranged  so  that  the  men  using 
it  as  a  shelter  are  enabled  to  fire  over  it  and  sweep 
the  ground  in  their  front  with  their  fire,  it  receives  the 
name  of  parapet,  a  word  derived  from  the  Italian 
[para,  petto,  defending  the  chest.] 

If  the  mass  is  not  arranged  for  this  purpose,  but 
simply  used  as  a  shelter,  it  is  called  an  epaulment. 

14.  Terreplein. — The  word,  terreplein,  is  used 
to  designate  the  surface  on  which  the  men  stand  in 
readiness  to  defend  the  parapet,  and  at  the  same  time 
are  screened  from  th^  enemy's  view.  The  terreplein 
may  be  the  natural  surface  of  the  ground,  it  may  be 
above  this  surface,  or  it  may  be  below  it,  as  the  bottom 
of  a  trench.  In  ordinary  field  fortifications  the  ter- 
replein is  the  natural  surface  of  the  ground. 

When  the  terreplein  is  above  the  natural  surface 
of  the  ground,  the  latter  is  termed  the  parade. 

15.  Profile. — The  form  and  dimensions  of  the 
profile   of  the  parapet  of  an   ordinary  field  fortifica- 


16  MELD  FORTlFtCATtONS. 

tion  are  represented  in  Figs.  1  and  2.  The  section 
A  B  C  D  E  F  is  the  profile  of  tlie  parapet ;  the  section 
G  H  J  K  is  the  profile  of  the  ditch  ;  and  both  together 
constitute  the  profile  of  the  fortification,  or  as  it  is 
generally  called,  the  profile. 

This  mass  of  earth  must  be  made  high  enough 
to  screen  the  men  on  the  terreplein,  A  P.  fi'om  the 
enemy's  view,  and  it  must  be  made  thick  enough  to 
intercept  his  missiles,  and  thus  afford  shelter  to  those 
behind  it 

When  this  mass  of  earth  has  a  height,  D  D'.  above 
the  ground,  of  over  four  feet  and  six  inches,  some 
arrangement  must  be  made  by  means  of  which  the 
defenders  can  deliver  their  fire  over  it  and  upon  the 
ground  in  front  of  it» 

This  is  provided  for  in  ordinary  field  fortifications, 
by  means  of  a  small  terrace,  B  C»  of  earth,  called  a 
banquette  J  placed  at  a  convenient  distance  below 
the  top  of  the  mass. 

The  upper  surface  of  this  terrace  is  called  the  ban- 
quette tread  and  is  connected  with  the  terreplein 
by  a  gentle  slope,  A  B.  called  the  banquette  slope. 
Sometimes  steps  are  used  instead  of  the  slope. 

Even  when  raised  high  enough,  the  soldier  would 
find  it  inconvenient  to  fire  over  the  mass  of  earth,  if 
it  be  left  in  the  condition  it  takes  when  first  heaped  up. 
The  U23per  surface  of  the  mass  is  therefore  sloped  off 
at   a   convenient   inclination,    and    joined   to   the  ban- 


GENERAL    PRIXCIPLES  A XI)    DEFJiC^rriONS.  17 


18  FIELD   FORTIFICATTO^S, 

quette  tread  by  a  slope,  against  which  the  soldier  caa 
lean  in  an  easy  position. 

This  upper  surface,  or  top  of  the  mass,  is  termed 
the  superior  slope,  and  the  surface  connecting  it 
with  the  banquette  tread  is  called  the  interior  slope. 
The  surface  connecting  the  superior  slope  with 
the  ground  in  front  is  called   the  eicterior   slope. 

16.  Benu. — The  horizontal  surface,  F  G,  which 
connects  the  exterior  slope  of  the  parapet  with  the 
ditch  is  called  the  berxn.  The  berm  coincides  with 
the  natural  surface  of  the  ground  in  ordinary  field 
fortifications. 

17.  Ditch. — The  ditch  may  have  almost  any  form 
of  cross-section.  The  usual  forms  are  triangular  or 
trapezoidal. 

The  surface  of  the  side  next  to  the  parapet  is 
called  the  scarp  •  the  surface  opposite  to  the  scarp 
is  called  the  counter-scarp, 

Sometimes  there  is  placed  a  mass  of  earth,  L  M  N, 
on  the  opposite  side  of  the  ditch,  with  the  upper  sur- 
face, M  N,  arranged  with  a  gentle  slope  to  the  front. 
This  gently  sloping  surface  is  called  a  glacis,  a  name 
also  applied  to  the  entire  mass  of  earth  so  arranged. 

18.  Crest,  foot,  etc. — Particular  names  are  given 
to  the  lines  of  intersection  of  the  surfaces  which  have 
just  been  mentioned  to  distinguish  them  from  each  other. 

The  intersection  of  surfaces  making  a  salient  angle 
with  the  plane  of  site  is  termed  a  crest  •  if  a  re-enter- 


ELEMENTS    OF  ORDINARY  PROFILE.  19 

ins:  ansfle.  it  is  called  a  foot:  and  each  intersection 
receives  a  characteristic  name  from  the  slope  to 
which  it  belongs.  Thus,  the  intersection  of  the  ban- 
quette slope  with  the  terreplein  is,  from  the  definition, 
a  foot ;  and  with  the  tread,  a  crest.  These  lines  are 
repectively  called  "the  foot  of  the  banquette  slope,'' 
and  ••  the  crest  of  the  banquette  slope." 

The  intersection  of  the  interior  slope  with  the 
superior  slope  is  simply  called  the  interior  crest* 
while  the  intersection  of  the  superior  slope  with  the 
exterior  slope  is  simply  called  the  exterior  crest ; 
all  others  following  the  rule  just  given. 

19.  Principal  lines  of  the  profile. — The 
principal  lines  cut  from  the  slopes  by  the  vertical 
plane  may  now  be  enumerated.  They  are  as  follows, 
(Fig.  1)  : 

The  site,   P  G  K  N. 

The  banquette  slope,  A  Bi 

The  banquette  tread,   B  Ci 

The  interior  slope,   C    D, 

The  superior  slope,    D   E. 

The  exterior  slope,    E  Fi 

The  berm,   F   6. 

The  scarp,   G  Hi 

The  bottom  of  the  ditch,    H  Ji 

The  counterscarp,  J   Ki 

The  interior  slope  of  the  glacis,  L  M,  and 

The  glacis,   M   N. 


20  FIELD   FORTIFICATIONS, 

These  lines  which  receive  the  names  of  the  surfaces 
from  which  they  are  cut,  intersect  in  points  common 
to  lines  of  the  parapet  and  ditch,  which  points  are 
known  as  follows  : 

The  foot  of  the  banquette  slope,  A, 

The  crest  of  the  banquette  slope,    Bi 

The  foot  of  the  interior  slope,  Ci 

The  Interior  Crest,  D. 

The  exterior  crest,   E, 

The  foot  of  the  exterior  slope.    Ft 

The  crest  of  the  scarp,   G. 

The  foot  of  the  scarp,   Hi 

The  foot  of  the  counterscarp,  J, 

The  crest  of  the  counterscarp,  Ki 

The  crest  of  the  glacis,   Mi 


CHAPTEE    III. 

DIMEl^^SIOKS   AND   INCLIN^ATION^S   OF    THE    LllS'ES    AI5"I) 
SLOPES    OF   AN   ORDINARY    PARAPET. 

20.  Height  of  parapet. — The  parapet  must  have 
a  height  sufficieatly  great  to  screen  its  defenders  from 
the  enemy's  view. 

A  man  standing  on  a  level  piece  of  ground  when  in 
the  act  of  aiming  his  gun  at  an  object,  does  not  fire 
at  a  higher  level  than  five  feet  above  the  ground  on 
which  he  stands.  A  parapet  five  feet  high  would  con- 
ceal from  his  view,  when  aiming  his  piece,  all  things 
behind  it  which  do  not  rise  above  this  height.  If 
the  height  is  less  than  five  feet,  the  parapet  would 
only  conceal  the  things  which  are  no  higher  than  it, 
and  then  only  by  placing  them  close  to  the  parapet. 

Taking  the  average  height  of  the  tallest  men  at 
six  feet,  the  parapet  should  have  a  height  of  at  least 
six  feet  and  six  inches  to  conceal  men  of  this  stature, 
when  walking  about  on   the  terreplein. 

From  these  two  conditions  the  following  principle 
has  been  stated,  for  determining  the  height  of  the  para- 
pet for  an  ordinary  field  fortification.  It  is  as  fol- 
lows :  The  lieigM  of  the  interior  crest  of  an  ordinary 
field  fortification  should  not  be  less  than  six  feet  and 


22  FIELD    FORTIFICATIONS. 

six  inches  above  the  site,  and  not  less  than  five  feet 
above  the  ground  occupied  by  the  enemy. 

The  labor  required  to  construct  a  parapet  increases 
rapidly  with  the  height.  A  height  of  twelve  feet 
is  considered  to  be  the  greatest  which  it  is  prac- 
ticable to  give  to  the  parapet  of  an  ordinary  field  for- 
tification. 

The  limits  are,  then,  six  and  one-half  feet,  and 
twelve  feet,  for  ordinary  fortifications. 

The  height  usually  taken  is  eight  feet,  and  this  is 
the  height  of  the  parapet  assumed  for  all  field  fortifi- 
cations, unless  otherwise  stated,  (Fig,  2.) 

The  settling  of  the  earth  after  the  parapet  has  been 
built ;  the  wearing  action  of  the  weather  ;  the  possible 
effect  produced  by  the  enemy's  projectiles ;  the  amount 
of  plunge  in  the  trajectories  of  those  missiles  which 
graze  the  interior  crests  ;  etc,  are  all  things  to  be  con- 
sidered, and  afford  good  reasons  for  selecting  eight 
feet  as  the  proper  height  to  be  used,  under  ordinary 
circumstances. 

21.  Command  and  relief. — The  height  of  the 
interior  crest  above  the  site  is  the  command  of  the 
work  ;  its  height  above  the  foot  of  the  scarp  is  the 
relief. 

The  term,  command,  is  also  used  to  express  the 
height  of  the  interior  crest  of  one  work  above  that  of 
another ;  or  above  any  particular  point  within  range. 

22.  Thickness  of  parapet. — Sufficient  thickness 


DIMEiYSIONS    OF  AN  ORDINARY  PARAPET,  23 

must  be  given  to  a  parapet  to  protect  those  behind  it 
against  the  enemy's  missiles.  The  thickness  of  a  para- 
pet is  the  horizontal  distance  between  the  interior  and 
exterior  crests.  This  of  course  must  be  greater  than  the 
penetration  of  the  enemy's  projectiles. 

The  kind  of  earth  used  in  building  the  parapet, 
the  penetration  of  the  enemy's  projectiles,  and  the 
probable  duration  of  the  enemy's  attack,  must  be  con- 
sidered in  determining  the  thickness  to  be  given  to 
the  parapet. 

The  rule  is  to  make  the  thickness  or  the  parapet 
one-half  greater  than  the  penetration  of  the  projec- 
tile into  the  same  kind  of  earth  as  that  of  which  the 
parapet  is  made.  The  amount  of  penetration  will  be 
different  for  different  earths  and  will  vary  with  the 
range,  the  calibre  of  the  guns,  and  with  the  kind 
of  projectile  used.  It  is  determined  by  experi- 
ment. 

Two  feet  is  about  the  limit  of  penetration  of  the 
the  bullet,  fired  from  the  rifled  musket,  at  close  range, 
into  ordinary  earth.  A  thickness  of  three  feet  will 
give  protection  against  musketry  fire. 

Six  feet  is  the  limit  of  penetration  into  ordinary 
earth  for  the  projectiles  of  field  guns.  Nine  feet 
would  be  the  thickness  to  give  to  a  parapet  intended 
for  protection  against  field  artillery.  As  this  is  the 
usual  fire  to  which  ordinary  field  fortifications  will  be 
exposed,   this  thickness  of   nine  feet  is  taken   to   be 


24  FIELD  FORTIFICATIONS. 

that  given  to  the  parapet,  (Fig.  2)  unless  otherwise 
expressed. 

It  is  well  to  remember  thg,t  it  is  far  better  to 
make  the  parapet  too  thick  than  not  thick  enougii 
Thus,  in  the  siege  of  Sebastopol,  in  1854,  the  French 
did  not  make,  in  the  beginning  of  the  siege,  a  proper 
allowance  for  the  increase  of  penetration  of  the  enemy's 
projectiles,  due  to  the  large  calibres  of  the  guns  used 
by  the  Russians.  The  result  was  that  the  siege  batteries 
and  powder  magazines  of  the  French  were  destroyed 
in  the  first  bombardment  A  similar  incident  occurred 
in  the  siege  of  Vicksburg,  in  1863,  where  a  battery 
constructed  by  the  besiegers  after  several  days  hard 
labor,  was  in  a  short  time  knocked  in  pieces  by  the 
heavy  projectifes  of  the  besieged. 

23.  Banquette. — The  banquette  is  a  device  by 
which  the  men  are  able  to  deliver  their  fire  over  the 
parapet.  It  is  made  just  high  enough  above  the  terre- 
plein  to  allow  men  of  medium  stature  to  fire  over  the 
interior  crest.  The  distance  of  the  tread  below  the  crest 
is  taken,  for  this  purpose,  at  four  feet  and  six  inches  ; 
sometimes  it  is  taken  three  inches  less,  or  four  feet 
and  a  quarter.  The  width  of  the  tread  depends  upon 
the  number  of  ranks  expected  to  occupy  it. 

In  the  days  of  smooth-bores  and  muzzle-loading 
muskets,  it  was  made  wide  enough  for  two  ranks. 
It  is  rarely  occupied,  at  the  present  time,  by  more 
than  one  rank. 


DIMUJSSIONS   OF  A^Y  ORDINARY  PARAPET,  25 

A  width  of  two  feet  is  sufficient  for  one  rank,  al- 
though it  is  usually  made  three  feet  wide  in  ordinary 
field  fortifications. 

The  tread  is  made  with  a  slope  to  the  rear,  to  allow 
the  water  falling  on  it  to  drain  off.  It  is  connected 
with  the  terreplein  either  by  a  slope  or  by  steps.  The 
inclination  of  the  former  is  usually  |- ;  it  may  be 
greater  if  the  banquette  is  low. 

When  steps  are  used,  the  tread  of  each  step  should 
not  be  less  than  twelve,  nor  more  than  eighteen,  inches  ; 
the  rise  should  not  be  less  than  nine,  nor  more  than 
twelve,  inches. 

Steps  are  generally  used  whenever  it  is  a  matter  of 
importance  to  gain  space.  All  other  things  being 
equal,  the  ramp  or  inclined  slope  is  preferred  to  steps. 

24,  Interior  slope. — It  would  be  desirable  to  make 
the  interior  slope  vertical  [and  it  is  oftentimes  made 
so]  for  the  reason  that  the  defenders  in  that  case  can 
stand  close  to  the  parapet  in  delivering  their  fire.  A 
vertical  slope  would  require  a  strong  construction  of 
some  kind,  to  retain  the  earth  in  position,  and  to  resist 
the  horizontal  thrust  produced  by  the  prism  of  rupture. 
When  the  materials  for  making  this  construction  are 
abundant  and  convenient,  a  vertical  slope,  or  one  nearly 
so,  may  be  used. 

Under  the  supposition  that  such  materials  are  not 
abundant  nor  convenient,  it  is  usual  to  give  an  inclina- 
tion to  the  slope,  which,  while  convenient  for  the  men 


26  FIELD   FORTIFICATIONS, 

to  lean  against,  will  require  only  a  slight  protection  to 
preserve  it. 

This  inclination  is  usually  taken  at  f  ;  an  inclina- 
tion which  nearly  coincides  with  that  of  the  plane  of 
rupture  of  ordinary  earths.  Earth  having  this  incli- 
nation, and  in  a  dry  state,  will  exert  little  or  no  hori- 
zontal thrust.  To  preserve  this  inclination,  it  will  only 
be  necessary  to  protect  it  against  the  weather,  or  to 
use  a  protection  strong  enough  to  hold  it  up,  when 
saturated  with  water.  This  protection  or  covering  is 
made  by  facing  the  slope  with  a  layer  of  stones,  of 
wood,  of  sods,  or  any  suitable  material  that  will  shed 
water,  or  be  strong  enough  to  resist  the  pressure,  when 
the  earth  becomes  saturated.  This  facing  is  called 
a  revetment. 

A  steep  slope  requires  a  strong  revetment,  other- 
wise it  is  to  be  preferred.  A  gentler  slope  requires 
a  slighter  protection,  but  has  the  disadvantage  of 
placing  the  soldier  too  far  from  the  interior  crest 
when  he  is  in  a  standing  position  ;  and  it  exposes  him 
more  to  projectiles  grazing  the  interior  crest. 

The  rarity  of  hand-to-hand  conflicts  on  the  parapet, 
and  the  use  of  breech-loading  weapons,  allow  the  use 
of  gentler  slopes  for  the  interior  of  the  work  than 
were  formerly  regarded  as  admissible.  Gentle  slopes 
are  accompanied,  however,  by  .the  disadvantage  of  re- 
quiring the  soldier  to  occupy  a  recumbent  position 
when  firing  his  piece. 


DIMENSIONS    OF  AN  ORDINARY  PARAPET.  ^7 

25.  Superior  slope. — The  upper  surface  of  the 
parapet  is  arranged  so  that  a  soldier  behind  the  in- 
terior crest  can  reach  with  his  fire  a  point  near  the 
crest  of  the  counterscarp.  This  line  of  fire  should 
pass  within  three  feet  of  the  crest  of  the  counterscarp, 
and  need  not  go  below  it.  By  this  arrangement,  the 
soldier  can  sweep  with  his  fire  all  the  ground  beyond 
the  ditch.  By  giving  the  superior  slope  an  inclina- 
tion of  \  (Fig.  2.)  it  will  be  found  that  this  condi- 
tion will  be  fulfilled  in  an  ordinary  field  fortification. 
If  the  line  of  fire  along  this  slope  does  pass  more 
than  three  feet  above  the  crest  of  the  counterscarp, 
the  inclination  must  be  increased.  The  angle  must 
be  limited,  because  as  it  is  increased,  the  weakness  of 
the  parapet  near  the  interior  crest  is  increased.  The 
limit  of  this  inclination  is  \, 

If  a  slope  of  -J  does  not  bring  the  line  of  fire  with- 
in three  feet  of  the  counterscarp,  the  inclination  can 
not  be  increased.  It  is  better  in  this  case  to  con- 
struct a  slight  glacis,  so  as  to  bring  the  assailants 
under  the  fire  of  the  parapet.  Care  must  be  taken 
that  the  upper  surface  of  the  glacis  is  kept  at  least 
five  feet  below  the  interior  crest  of  the  work. 

It  is  well  to  state  that  a  slope  for  the  upper  sur- 
face of  the  parapet  is  a  necessary  evil.  It  weakens 
the  parapet  by  making  it  thin  near  the  interior  crest, 
and  this  thin  portion  wears  away  quickly  under  the 
action  of  the  weather  and  the  enemy's  fire.     Still,    if 


28  FIELD  FORTIFICATIONS. 

it    had  no    slope,   it  would  mask    the    enemy  when 
near  the  work. 

26.  Exterior  slope. — From  the  outer  edge  of 
the  superior  slope,  the  earth  takes  its  natural  slope. 
This  is  supposed  to  be  at  an  angle  of  about  forty- five 
degrees  with  the  horizontal.  The  inclination  of  the 
exterior  slope  is  therefore  assumed  to  be  \  (Fig.  2) 
unless  otherwise  stated. 

In  practice  it  is  recommended  to  make  this  slope 
about  ^,  or  even  f ,  since  it  is  exposed  directly  to  the 
fire  of  the  enemy,  and  receives  the  drainage  from  the 
superior  slope. 

27.  Berm. — The  natural  surface  of  the  ground 
between  the  foot  of  the  exterior  slope  and  the  crest  of 
the  scarp  forms  the  berm,  in  field  fortifications.  Its 
width  depends  upon  various  circumstances,  but  prin- 
cipally upon  the  character  of  the  soil.  It  is  recom- 
mended to  place  the  foot  of  the  scarp  upon  the  pro- 
longation of  the  exterior  slope.  The  width  of  the 
berm  will  therefore  depend  upon  the  inclination  given 
to  the  scarp  and  the  depth  of  the  ditch.  The  steeper 
the  slope  of  the  scarp,  the  wider  will  be  the  berm. 

As  a  matter  of  defence,  the  berm  is  considered  to 
be  a  defect,  since  it  offers  advantages  to  the  assailant 
in  assaulting  the  work. 

It  is  nevertheless  a  useful  part  during  the  con- 
struction of  a  work,  as  it  forms  a  bench  upon  which 
the  earth  from   the   ditch  can  be  thrown,   and  upon 


DIMENSIONS   OF  AN  ORDINARY  PARAPET,  29 

which  workmen  can  stand  to  throw  this  earth  upon  the 
parapet.  It  is  also  useful  in  reducing  the  wearing  effect 
of  the  wash  upon  the  scarp,  due  to  the  water  running 
off  the  superior  slope,  and  down  the  exterior  slope. 

28.  Ditch. — The  primary  object  of  the  ditch  is 
to  furnish  enough  earth  to  build  the  parapet.  The 
height  and  thickness  of  the  parapet  having  been  as- 
sumed, the  cubical  contents  are  easily  calculated,  and 
the  dimensions  of  the  ditch  determined. 

It  is  a  principle  belonging  to  the  art  of  fortifica- 
ion,  that  everything  used  in  the  defence  of  a  position 
should,  when  practicable,  be  arranged  so  as  to  be  more 
or  less  of  an  obstruction  to  the  advance  of  the  enemy. 
The  ditch  should  therefore  be  arranged  so  as  to  be 
an  obstruction  to  the  enemy's  assault. 

A  ditch,  not  less  than  six  feet  deep  and  twelve 
feet  wide,  is  an  obstruction  not  easily  passed.  A 
ditch  of  less  dimensions  would  not  offer  much  of  an 
obstruction   to  an  assaulting   column. 

Ditches  deeper  than  twelve  feet  are  rarely  con- 
structed, in  consequence  of  the  amount  of  labor  re- 
quired to  dig  them. 

Within  these  limits  of  twelve  and  six  feet  deep, 
a  ditch  can  be  dug  which  will  give  the  necessary 
amount  of  earth  and  be  at  least  twelve  feet  wide, 
thus  offering  a  respectable  obstacle  to  an  enemy's  as- 
sault. 

In  small  ditches,  it  is  recommended  to  make  them 


30  FIELD   FOUTfFrCATIONS. 

with  a  triangular  cross  section,  in  this  way  getting  the 
greatest  possible  depth  and  width  for  the  ditch. 

In  the  profile  (Fig.  2.)  the  ditch  is  trapezoidal  in 
cross-section,  with  a  depth  of  seven  feet,  and  a  width 
at  bottom  of  ten  feet. 

29.  Scarp  and  Counter-scarp. — The  width  at 
the  top  of  the  ditch  is  affected  more  or  less  by  the 
inclination  given  to  the  sides  of  the  ditch.  The 
slopes  of  the  counterscarp  and  scarp  vary  between 
wide  limits,  and  depend  upon  the  kind  of  soil,  upon 
the  depth  of  the  ditch,  the  amount  of  obstruction 
the  ditch  is  expected  to  give,  etc.  All  things  being 
equal,  the  slopes  are  made  as  steep  as  they  will  stand  ; 
and  if  required  to  last  for  some  time,  they  should  be 
protected  by  a  revetment.  In  the  ordinary  profile 
(Fig.  2)  they  are  taken  at  \  for  the  scarp,  and  f  for 
the   counterscarp. 

30.  Calculation  used  to  determine  the 
dimensions  of  the  ditch. 

The  height  and  thickness  of  the  parapet  having 
been  assumed,  the  dimensions  of  the  ditch  may  be 
obtained  by  the  following  method,  which  is  practi- 
cally that  given  in  the  "  Aide-Memoire,"  for  engi- 
neers of  the  French  army. 

Denote  by 

R,  the  volume  of  the  parapet. 

S,  the   area   of    the    profile    of    the   parapet,,  and 

Z,  the  right  line  generated  by  the  centre  of  gravity 


DIMENSIONS    OF  AN  ORDINARY  PARAPET.  ol 

of  the  profile  of  the  parapet,  supposing  this  profile 
moving  parallel  to  itself,  and  generating  the  volume 
of  the  parapet  under  consideration. 

Denote  by 

R',    S',    and   V,    similar   quantities  for  the    ditch. 

The  volumes  for  the  parapet,  and  the  ditch,  for 
any  part  of  the  work  under  consideration,  will  be 
expressed  as  follows, 

E  =z  S  X  I     and     R'  =  S'   ^   l'    .    .    .     (1) 

Earth  when  made  into  an  embankment  occupies 
a  greater  space  than  it  did  in  the  natural  state.  De- 
note   this  increase  of   volume  bv    — .     Since   the   vol- 

771 

ume  of  the  earth  in  embankment  is  furnished  by 
the  volume  excavated   from   the   ditch,    there   results, 

M=i^-  r^-^ (3) 


Substituting    in   equation    (2)    the   values  taken   from 
eqs.    (1),    there   results, 

m    \ 
m^-l) (3> 

It  will  be  sufficiently  exact  to  take  r  equal  to  the 
length  of  the  middle  line  of  the  ditch  ;  which  being 
substituted,  gives  JS^  in  known  terms. 

Suppose  the  scarp  to  have  a  slope  of  |,  and  the 
counterscarp   a   slope   of    f.     Kepresent  the   width   of 


32  FIELD   FORTIFICATIONS. 

the  ditch  at  top  by  x,  and  its  depth  at  the  middle 
by  y.  Denote  the  angle  of  the  natural  slope  by  </>. 
Using  this  notation,  the  area  of  the  profile  of  the 
ditch,  is  given  as  follows, 


S'  =y      (x  -  ^  y  cot.    ^ 


(4) 


Solving  eq.  (4)  with  respect  to  x,  there  results, 

7                       S 
«  =  12  ^  cot-  ^  +  V  ' ^^^ 


and  solving  with  respect  to  «/,  and  taking  the  minus 
sign  of  the  radical,  ic  gives 


y   tan.  ^  [x --  y'j.i  _    7  ^'  coi.  ©  V 


(6) 


From  these  equations  (5  and  6)  y  can  be  assximed, 
and  X  deduced  ;  or  x  assumed,  and  y  deduced. 

Making  ^  =  45°,    these   last  equations  reduce  to 

# 


«  =  12  ^  "^   "7  '     and 


It  should  be  remembered  in  assuming  values  for 
X  and  y.  that  x  must  not  be  less  than  twelve  feet, 
and  y  not  less  than  six,  nor  greater  than  twelve  feet. 

31.  In  practice,  it  will  be  sufficiently  accurate  to 
calculate  the  area  of  the  assumed  profile,  assume  a 
depth  for  the  ditch,  and,  without  making  an  allowance 


DIMENSIONS   OF  AN  ORDINARY  PARAPET,  33 

for  the  increase  of  volume  of  the  earth  in  the  embank- 
ment, divide  the  area  of  the  profile  by  the  assumed 
depth  of  the  ditch.  The  result  will  give  the  width  of 
the  ditch. 

32.  Normal  profile.— The  profile  (Fig.  2)  with 
the  dimensions  and  inclinations  just  mentioned  is  some- 
times called  the  normal  profile  of  field  fortifications. 
It  is  the  profile  which  would  be  constructed  for  a  work 
located  upon  a  level  site,  and  when  there  is  time  to 
build  it. 

It  is  evident  that  great  variations  must  occur, 
influenced  largely  by  the  kind  of  earth  and  the  sur- 
rounding circumstances  at  the  time  of  construction. 

Slopes  which  are  practicable  in  one  kind  of  earth 
will  not  retain  their  shapes  in  other  kinds. 

Parapets  placed  on  sites  commanding  all  ground 
in  common  range  need  not  be  so  high  as  those  on  lower 
ground  commanded  by  neighboring  heights. 

The  principles  laid  down  and  the  reasons  expressed 
for  the  normal  profile  apply  equally  well  to  all  its 
variations. 


CHAPTER    IV. 

THE   TRACE   OF   A    FIELD   FORTIFICATION. 

33.  Trace.— The  term,  trace,  is  used  by  military 
engineers  to  denote  the  plan,  or  the  general  outline,  of 
a  field  fortification  upon  the  ground.     (Art.  11.) 

In  field  fortifications  the  governing  or  principal  line 
used  constructing  the  trace  is  the  projection  upon  the 
plane  of  site,  of  the  line  from  which  the  fire  is  deliv- 
ered, viz,  the  interior  crest. 

The  projection  of  the  interior  crest  upon  the 
ground  is  called  the  sub-crest. 

34.  £[inds  of  fire. — The  trace  of  a  field  for- 
tification can  not  be  marked  intelligently  upon  the 
ground,  until  the  positions  which  the  enemy  may 
possibly  occupy,  and  the  kinds  of  fire  he  can  bring 
to  bear,  are  known. 

Different  names  are  used  to  designate  the  fire, 
both  of  artillery  and  musketry,  depending  upon  its 
direction  and  kind. 

The  terms,  front,  reverse,  flank,  and  cross 
fires  are  used  to  designate  the  direction  of  the  fire 
with  respect  to  the  line  aimed  at.  The  projectile 
striking  the  line  in  front,  or  in  rear,  or  at  its  ex- 
tremities,   or    crossing  in    its    flight  other   projectiles 


TRACK    OF    A    FIELD    FORTIFICATION.  35 

coming*  from  a  different  direction,  gives  the  name  to 
the  kind  of  fire  to  which  the  line  is  exposed. 

When  the  direction  of  the  fire  is  perpendicular^  or 
nearly  so,  to  the  line  aimed  at,  the  fire  is  a  direct 
one ;  if  this  direction  makes  an  angle  with  the  line 
aimed  at,  it  is  oblique ;  if  this  angle  is  very  slight, 
it  is  a  slant  fire  ;  if  no  angle  is  made  bnt  the  di- 
rection coincides  with  the  prolongation  of  the  line 
aimed  at,  it  is  an  enfilading  fire  ;  if  it  makes  no 
angle,  but  is  in  front  of  the  line,  it  is  called  a 
flanking   fire  ;  etc. 

A  line  of  troops  or  a  line  of  parapet  may  be  exposed 
to  a  front  direct  fire,  a  reverse  fire,  a  slant  fire,  a  slant 
reverse  fire,  an  enfilading  fire,  a  cross  fire,  etc.  A 
column  of  troops  might  be  exposed  to  a  front  direct, 
an  oblique,  a  flank,  a  reverse,  or  a  cross  fire,  ac- 
cording to  the  directions  from  which  the  projectiles 
came. 

Other  designations  are  used  to  denote  the  hinds  of 
fire.  Thus,  a  direct  or  pitching  fire  means  one  in 
which  the  projectile  is  fired  from  a  gun  at  ordinary 
elevations,  and  with  the  service  charge ;  a  curved 
fire,  when  the  angle  of  elevation  is  greater  than  usual, 
and  the  amount  of  charge  used  in  the  gun  is  less  ;  a 
vertical  fire,  when  the  angles  of  elevation  are  still 
larger. 

Other  designations  denote  the  kind  of  fire,  as  de- 
termined  by  the   position  of    the  line  of  fire  with  re- 


36  FIELD  FORTIFICATIONS. 

spect  to  the  surface  aimed  at,  or  some  peculiar  char- 
acteristic which  marks  it.  Thus,  a  ricochet  fire,  is 
the  result  produced  by  small  angles,  low  charges,  and 
spherical  shot ;  a  grazing  fire  is  when  the  projectile 
passes  very  near  the  surface ;  a  plunging  fire,  when 
the  projectile  comes  from  a  higher  level  than  that 
occupied  by  the  object  struck  ;  etc. 

35.  Salients  and  re-entrants. — An  assailant 
when  attacking  a  field  work  naturally  tries  to  advance 
over  that  ground  which  offers  the  least  obstruction  to 
his  free  movements,  and  which  does  not  expose  him 
to  the  fire  of  the  defenders.  In  the  latter  case,  the 
most  favorable  ground  will  be  that  upon  which  the 
defence  cannot  bring  a  fire,  and  the  most  unfavorable, 
will  be  that  upon  which  th^  defence  can  bring  a  cross 
fire. 

In  order  to  have  an  effective  direct  fire  upon  the 
ground  exterior  to  the  parapet,  the  interior  crest 
should  be  perpendicular,  or  nearly  so,  to  the  direction 
in  which  the  fire  is  to  be  thrown.  And  since  there 
are  several  directions  in  which  the  fire  is  wanted,  it 
follows  that  the  interior  crest  must  be  a  broken 
line. 

Those  angles  of  the  interior  crest  which  project 
outwards,  and  towards  the  enemy,  are  called  salient 
angles ;  those  projecting  inwards,  are  called  re-en- 
tering angles. 

36.— General   principles.    The  following  gen- 


TRACE   OF   A    FIELD  FORTIFtCATtON,  37 

er;ii  principles    should  govern  the   engineer  in  the  se- 
lection  of  the   trace. 

1.  The  trace  should  be  as  simple  as  possible. 

2.  The  direction  of  the  interior  crest  should  be 
such  as  to  admit  of  bringing  a  strong  direct  fire 
upon  the  ground  liable  to  be  occupied  by  the  enemy. 

3.  The  dimensions  of  the  works  and  interior  space 
should  be  proportioned  to  the  number  of  men  in- 
tended to  defend  them. 

4.  The  principal  lines  of  a  fortification  should  be 
given  such  directions  that  they  cannot  be  easily  en- 
filaded, nor  seen  in  reverse. 

5.  No  salient  angle  should  be  less  than  60°. 

37.  That  the  trace  should  be  simple  is  evident. 
Field  fortifications  are  works  which  are  to  be  con- 
structed in  a  short  time  and  under  pressing  circum- 
stances. Multiplicity  of  details  and  refinements  of 
construction  would  cause  a  waste  of  valuable  time,  a 
thing  of  far  greater  importance  in  a  campaign  than 
theoretical  perfection. 

A  strong  direct  fire  is  obtained,  as  previously 
stated,  by  placing  the  line  of  the  interior  crest  as 
nearly  perpendicular  as  possible  to  the  direction  in 
which  the  fire  is  to  be  delivered.  A  small  deviation 
is  admissible,  depending  upon  the  advantages  to  be 
derived  from  changing  the  position  of  the  line. 

The  work  should  be  proportioned  so  as  not  to  re- 
quire  more  men   to  defend  it   than   are  available.     A 


38  FIELD  FORTIFICATIONS. 

fortification  is  a  passive  defence,  and  is  an  inert  and 
helpless  factor,  if  not  defended  by  a  live"  and  active 
force. 

It  is  not  always  practicable  to  arrange  the  lines  so 
as  to  satisfy  the  second  and  the  fourth  conditions  at 
the  same  time.  To  comply  with  the  former  would 
be,  in  many  cases,  to  expose  the  line  to  the  fire  con- 
demned by  the  fourth  condition.  The  fourth  con- 
dition must,  under  such  circumstances,  be  satisfied  by 
some  expedient  which  will  annul  the  effects  of  the 
enfilade  fire.  The  expedients  generally  used  are  tra- 
verses. Their  employment  and  construction  will  be 
explained  hereafter. 

Angles  of  less  than  60°,  for  salients,  restrict  the 
interior  space,  and  do  not  leave  sufficient  room  to 
serve  the  guns  which  may  be  used  in  the  salients ; 
they  also  weaken  the  earth  work  of  the  parapet  at 
these  points. 

It  may  not  be  possible  to  have  the  trace  fulfil  all 
these  conditions.  If  it  does,  and  if  the  profile  of  the 
parapet  is  a  strong  one,  the  fortification  will  be  a 
good  one  and  will  prove  a  formidable  obstacle  in  the 
enemv's  wav. 


CHAPTER    V. 


FIELD     WORKS. 


38.  Field  -works  and  lines.— Field  fortifica- 
tions are  usually  divided,  according  to  the  extent  of 
the  position  fortified,  into  two  general  classes,  viz.  : 
field  works,  and  lines. 

The  term,  field  work,  is  applied  to  the  temporary 
fortification  used  to  strengthen  a  position  of  limited 
extent,  and  in  which  the  troops  occupying  it  are  ex- 
pected to  be  dependent  upon  themselves  alone  for  a 
successful  resistance  to  an  assault. 

The  term,  line,  is  applied  to  the  temporary  for- 
tification, or  chain  of  fortifications,  which  is  used  to' 
strengthen  a  position  of  considerable  extent,  and  is 
to  be  defended  by  an  army  or  a  large  body  of 
troops. 

These  two  classes  of  fortification  do  not  differ  as 
to  the  details  of  their  construction. 

39.  Classes  of  field  -works. — The  trace  of  a 
field  work  depends  upon  the  directions  in  which  it 
has  to  fire.  (Art.  34.)  It  may  have  to  fire  on  all  sides 
of  the  position  ;  or  over  a  limited  portion  of  a  circle  ; 
or  in  special  directions  only,  according  to  the  posi- 
tions which   may    be   occupied    by  the   enemy's   artil- 


4U  FIELD   FORTIFICATIONS. 

iery.     These  different  circumstances  give  rise  to  three 
kinds  of  field  works,  viz.  : 

1.  Field  works  exposed  to  the  artillery  fire  of  the 
enemy  in  one  direction  only,  or  in  front ; 

2.  Field  works  exposed  to  artillery  fire  of  the 
enemy  on  the  flanks  as  well  as  in  front ;   and 

3.  Field  works  exposed  to  this  fire  upon  all  sides 
of  the  position. 

It  is  evident  that  in  the  trace  of  a  work  of  the 
first  kind,  the  position  which  the  enemy  may  have  in 
its  front  need  only  be  considered. 

The  trace  of  a  work  of  the  second  kind  must  be 
considered  under  the  supposition  that  the  enemy  may 
appear  in  front  and  on  the  flanks,  that  is  in  a  por- 
tion bounded  by  a  part  of  a  circle. 

The  trace  of  a  work  of  the  third  kind  must  be 
considered  under  the  supposition  that  the  enemy  may 
appear  on  all  sides  of  the  work. 

It  is  plain  that  parapets  are  needed  on  all  sides, 
in  the  works  of  the  third  kind,  to  shelter  the  men 
from  the  enemy's  fire  ;  and  that  they  are  only  needed 
on  the  exposed  sides,  in  works  of  the  first  and  second 
kinds.  The  works  of  the  first  and  second  kinds  may 
then  be  left  open  on  the  sides  not  exposed  to  artil- 
lery fire,  or  they  may  be  closed  by  some  obstruction. 
From  the  construction  of  the  parapets,  in  these  dif- 
ferent cases,  there  arise  three  classes  of  field  works, 
viz.  :  open,  half-closed,  and  closed  works. 


FIELD    WORKS,  41 

40.  Open,  and  half-closed  works. — A  simple 
straight  line  of  parapet  is  an  example  of  an  open  field 
work.  It  is  plain  that  a  work  of  this  kind  would  only 
be  used  where  it  would  be  impossible  for  the  enemy 
to  get  on  the  flanks,  or  around  in  its  rear ;  or  where 
it  is  intended  to  abandon  it  as  soon  as  the  enemy 
approaches. 

Half-closed  works  are  used  where  there  is  any  dan- 
ger of  the  enemy  appearing  suddenly  upon  the  flanks. 
They  are  closed  by  some  obstruction  so  as  to  prevent  a 
surprise  or  sudden  attack  by  small  bodies  of  infantry 
that  might  appear   suddenly  in  rear  of  the  position. 

One  of  the  simplest   forms  of  the  half-closed  field 
work  is  the  redan,  (Fig.  3.)    It        Fig.  3, 
consists    of   two    straisrht    lines  /. 

forming  an  angle  BAG,  which  / 

is  pointed   towards   the   enemy.         / 

The   angle  at    A    is  called   the  bZ. 

salient ;    the  sides   B   A    and 

C  A  are  called  the  faces ;   the  line  B  C  is  termed  the 

gorge  ;  the  line   A  D  is  called  the  capital. 

The  sides  of  the  redan  are  usually  from  thirty  to 
sixty  yards  long.  When  the  length  is  less  than  thirty 
yards  it  is  called  a  fl^che. 

The  redan,  as  here  shown,  delivers  its  fire  over  a 
part  of  a  circle  but  has  no  front  fire.  If  it  be  necessary 
to  have  a  fire  in  the  direction  of  the  capital,  it  may  be 
obtained  by  using  the  blunted  redan^  which  is  con- 


^2 


FIELD   FORTIFICATIONS, 


structed  by  stopping  the  faces  at  points,  as  E  and  p 
and  connecting  these  points  by  a  straight  parapet. 
Two  redans  are  sometimes  placed  side  by  side  and 
joined  to  each  other,  making  a  work  known  as  the 
double  redan ;  sometimes  the  outer  faces  of  the 
double  redan  are  made  much  longer  than  the  faces 
which  are  connected,  in  which  case  the  work  re- 
ceives the  name  of  priest-cap,   or  STvallow-tail. 

41.  Lunettes. — If  to  a  redan  lines  of  jDarapet  are 
added  which  are  parallel,  or  nearly  so,  to  the  capital, 
the  construction  will  be  that  known  as  a  lunette, 
(Fig.  4.) 

These  parts,  B  C  and  D  E 
which  were  added  to  the  redan, 
BAD,  are  termed  the  flanks  ; 
the  angles,  at  B  and  at  D  are 
iE  called  shoulder  -  angles.  A 
lunette  is  therefore  a  field  work 
consisting  of  two  faces  and  two  flanks. 

42.  Bastioned    Front. — Suppose   two    lunettes, 

Fig.  5. 

^ 


A  and  B  to  be  connected   by  a  straight  line  of  parapet, 
C  D  (^ig-  ^)      '^"^^^  resulting  construction    is    called  a 


FIELD    WORKS.  43 

bastioned  trace,  and  the  portion  between  the  capi- 
tals through  E  ^i^d  F  a  bastioned  front.  The  lun- 
ettes when  thus  joined  are  called  bastions  ;  the  line 
of  parapet  joining  them  is  the  curtain  ;  and  the  re- 
entering angles  ac  C  and  D  are  known  as  the  cur- 
tain angles. 

43.  Closed  works. — Since  the  works  of  this  kind 
are  exposed  to  the  enemy's  fire  of  artillery  on  all  sides, 
the  position  must  be  entirely  surrounded  by  a  parapet. 
The  trace  of  such  a  work  may  be  of  any  form,  either 
circular,  square,  quadrilateral,  polygonal — regular  or 
irregular — all  salient  angles,  or  some  salient  and  some 
reentering  angles. 

A  closed  work  in  which  all  the  angles  are  salients 
is  called  a  redoubt  ;  if  there  are  reentering  angles,  it 
is  termed  a  fort. 

44.  Redoubts. — A  redoubt  may  be  of  any  figure 
provided  it  has  no  reentering  angles.  Circular  re- 
doubts are  sometimes  used,  but  are  objected  to  on 
account  of  the  divergence  of  their  fire.  Redoubts  are 
usually  polygonal  in  plan,  and,  on  horizontal  sites, 
there  is  no  reason  why  the  plan  should  not  be  a  regu- 

Fig.  6. 


lar   figure.      The   most   simple    and    the   most   usually 
employed  figure  is  the  square,  (A  Fig.  6). 


44  FIELD  FORTIFICATIONS. 

The  redoubt,  B  (Fig.  6)  is  a  form  which  is  fre- 
quently used  when  it  is  desirable  to  combine  its  6re 
to  the  front  with  that  coming  from  other  points  to 
the  right  and  left  of  it,  and  still  keep  a  direct  fire 
on  the  flanks. 

The  advantages  claimed  for  redoubts  over  forts 
are  simplicity  of  trace,  ease  of  adaptation  to  irregu- 
lar sites,  less  labor  required  in  their  construction, 
and  fewer  men  are  necessary  to  defend  them  for  the 
same  amount  of  space  enclosed. 

45.  Star  forts. — A  fort  of  this  class  receives  its 
name  from  the  general  resemblance  which  its  trace 
has  to  the  conventional  symbol  used  to  represent  a 
star.  The  star  of  six,  or  of  eight,  points  is  the  kind 
mostly  employed,  although  any  number  of  points  may 
be  used,  being  determined  ordinarily  by  the  confor- 
mation of  the  ground  on  which  it  is  built.  The 
construction  of  the  trace  of  a  six  pointed  star  is  as 
follows : 
Fig.  7,  A  Describe   an   equilateral    triangle  ; 

/       \  trisect  its  sides  ;    on  the  middle   por- 

\  /  \  /    tion  of  each  side,  determined  by  this 

/\  /\     trisection,    construct     an     equilateral 

\~     ~y  triangle.       The     resulting     construc- 

V  tion    gives    the    six-pointed     star,    as 

shown  by  the  full  lines  in  Fig.  7. 

The  trace  of   the  eight-pointed  star  is  constructed 

in  a  similar  manner,  using  a  square  instead   of  the 


FIELD    WORKS. 


45 


equilateral   triangle    as    the    preliminary   figure.     The. 
construction  is  as  follows  : 

Describe  a  square  ;  trisect  its  sides,  and  construct 
equilateral  triangles  on  the  middle  portions  thus  de- 
termined (Fig.  8) ;  or,  what  is  a  better  trace,  replace 
the  right  angles  of  the  square  by  angles  of  60°,  as 
shown  at  A  ^^  the  lower  half  of  Fig.  8. 

46.  Bastloned  fort. — 
If  the  space  to  be  enclosed 
is  circumscribed  by  a  poly- 
gon, and  on  each  of  the  sides 
a  bastioned  front  (Fig.  5) 
is  constructed,  the  resulting 
work  is  called  a  bastioned 
fort. 

The  polygon  used  to  enclose  the  space  to  be  de- 
fended may  have  any  number  of  sides,  and  may  be 
either  a  regular  or  an  irregular  figure.  On  a  hori- 
zontal site,  there  is  no  reason  why  the  figure  may  not 
be  a  regular  polygon. 

On  a  level  site,  the  polygon  generally  used  is  a 
square  unless  a  larger  work  is  required. 

The  construction  of  the  trace,  when  the  circum- 
scribing polygon  is  a  square,  is  as  follows  : 

Let  A  B  (Fig.  9)  be  one  of  the  sides  of  the  cir- 
cumscribing square.  Bisect  this  side  and  at  its  mid- 
dle point,  C  erect  a  perpendicular,  C  P  ^.nd  lay  off 
a  distance  C   P  equal  to  one-eighth   of  A   Bi      J^ii^ 


40 


FIELD   FORTIFLCA  TIOXS, 


the  point  p  thus  determined  with  the  ends,  A  a^d  B, 
of   the   side  of   the   square.      Lay   off   from   A  '^^^  B, 


Fig.  9 

h 


1\  N         — -----.G 


16 

p, —"^ 


on  the  lines  H  P,  ^^^^^  B  P,  the  distances  A  G  ^'^ti 
B  H,  each  equal  to  two-sevenths  of  A  B.  Draw 
through  G  the  lii^e  G  F,  so  that  the  angle  G  F  B 
shall  not  be  less  than  90°,  nor  greater  than  110% 
and  produce  it  until  it  intersects  the  line  B  P  pi'o- 
longed.  Do  the  same  at  H,  so  that  the  angle  H  D  A 
shall  fall  within  these  limits  just  named.  Join  tlie 
points  F  ^^^  D  thus  determined  by  a  straight  line. 
The  line  A  G  F  D  H  B  will  be  the  trace  of  a  bastioned 
front  constructed  upon  the  side  A  B  of  the  circum- 
scribing  square.      Do    the    same   for   the   other    three 


FIELD   TFO^^^^jvEBSITYjl    47 

sides  of  the  square,  and  the  resw^ik^^^^^bfuction  is 
the  trace  of  a  bastioned  fort. 

In  a  similar  manner  the  construction  is  made  for 
a  bastioned  front,  when  the  polygon  has  a  greater 
number  of  sides  than  four.  The  only  variation  made 
is  in  the  length  of  the  distance  C  P,  ^^is  distance 
being  taken  one-seventh  of  the  side  of  the  polygon 
instead  of  one-eighth,  when  the  circumscribing  poly- 
gon is  a  pentagon  ;  and  one-sixth,  when  the  polygon  is 
a  hexagon  or  a  polygon  of  a  greater  number  of  sides. 

It  is  evident  that  the  triangle  can  not  be  used  for 
the  circumscribing  polygon.  If  it  were,  the  fifth  con- 
dition for  field  works  (Art.  36)  could  not  be  satisfied. 

47.  Nomenclature. — The  side  of  the  circum- 
scribing polygon  is  called  the  exterior  side  ;  the 
line,  C  P,  is  called  the  perpendicular  ;  the  lines 
D  A  and  F  B?  the  lines  of  defence  ;  the  angles 
GAG  and  H  B  G  are  called  the  diminished  ang- 
les. The  other  parts  are  named  as  already  stated  in 
articles  40,  41,  and  42. 

48.  Sectors  without  fire,  and  dead  spaces. 
— The  star  and  bastioned  forts  were  devised  to  remedy 
the  defects  of  sectors  without  fire,  and  of  dead  spaces, 
which  are  found  in  redoubts. 

A  sector  without  fire  is  the  name  given  to 
that  space  exterior  to  a  work  which  is  not  defended 
by  the  direct  fire  of  the  adjacent  faces.  Thus, 
the  faces  A  B  and  A   G  of  the  redan   (Fig.   3)   or  the 


48  FIELD  FORTIFICATIONS. 

faces  A  B  and  A  D  of  the  lunette  (Fig.  4)  or  the  faces 
of  any  salient,  if  prolonged  to  the  exterior,  would  in- 
clude a  space  not  exposed  to  a  direct  fire  from  the 
adjacent  faces.  This  included  space  is  in  a  great 
measure  undefended,  except  by  a  very  oblique  fire, 
so  far  as  the  faces  are  concerned.  This  is  the  space 
known  as  the  sector  without  fire. 

Any  ground,  over  which  the  defenders'  fire  may 
pass,  but  so  high  above  the  assailant  that  he  can  not 
be  injured  by  it,  is  called  a  dead  space,  or  a  dead 
angle.  Thus,  in  the  redan  or  the  lunette  just  men- 
tioned, if  the  enemy  gets  into  the  ditch,  he  is  safe 
from  any  fire  coming  over  the  parapet.  The  ditch 
in  each  of  these  cases  has  the  defect  known  as  a  dead 
space. 

It  was  to  remedy  these  defects,  which  exist  in  all 
works  where  the  angles  are  all  salients,  that  parts 
of  a  work  were  drawn  back,  or  made  to  form  re- 
entering angles,  for  the  purpose  of  arranging  lines 
from  which  direct  fires  could  be  brought  to  bear  upon 
the  ground  not  defended  by  the  lines  adjacent  to  it. 

49.  Flanked  disposition.  The  arrangement  of 
lines  by  which  direct  fires  are  brought  to  bear  upon 
sectors  without  fire,  and  by  means  of  which  dead 
spaces,  are  reached  by  a  fire  from  the  parapet,  is  called 
a  flanked  disposition.  This  term  is  used  to  de- 
note this  arrangement,  because  the  enemy  advancing 
upon  a  salient,  where   this    arrangement    is    used,    is 


FIELD    WORKS.  49 

exposed  to  a  flanking  fire — a  fire  parallel  to  and 
in  front  of  the  line  attacked.  (Art.  34,) 

The  defects  of  a  flanked  disposition  are  :  the  ex- 
posure of  the  lines  of  the  work  to  enfilading  or  re- 
verse fires ;  a  contraction  of  the  space  enclosed  by 
the  work ;  and  a  partial  sacrifice  of  the  strong  direct 
fire  which  the  work  might  otherwise  have. 

A  convergence  or  a  crossing  of  fires  upon  the 
ground,  which  can  be  obtained  by  a  flanked  disposi- 
tion at  certain  points,  is  productive  of  demoralization, 
as  well  as  severe  loss,  among  troops  exposed  to  it. 
For  this  reason,  a  flanked  disposition  was  formerly 
laid  down  as  an  essential  element  to  be  incorporated 
in  all  schemes  of  defence.  It  is  still  an  important 
factor.  But,  in  the  use  of  the  long  range  weapons 
now  employed,  the  strong  direct  and  front  fire  is 
considered  to  be  so  important,  that  it  is  thought 
best  not  to  sacrifice  any  part  of  it,  if  it  can  be 
avoided.  Especially  is  this  so  when  the  advantage 
to  be  gained  is  accompanied  by  the  defect  of  ex- 
posing some  of  the  lines  of  the  work  to  an  enfilading 
fire. 

An  important  advantage  claimed  for  the  flanked 
disposition,  is  its  ability  to  sweep  its  own  ditches  by 
fires  from  the  work  itself.  In  field  works,  the  ditches 
are  too  narrow,  and  their  depth  too  slight,  to  make 
this  a  matter  of  great  importance,  when  compared  with 
the  defects  which  accompany  the   flanked   disposition. 


60  FIELD  FORTIFICATIONS. 

Still,  in  iield  works,  especially  in  the  case  of  a  large 
independent  work,  or  a  work  which  occupies  the  key 
point  of  an  important  position,  the  ditches  should  noc 
be  left  undefended.  They  may  be  flanked  by  inde- 
pendent defences  placed  in  the  ditch — an  expedient 
which  will  be  explained  hereafter. 

50.  Relation  between  the  parts. — An  in- 
timate relation  exists  between  the  different  parts  of  a 
flanked  disposition.  These  are  so  connected  that  a 
change  in  any  one  affects  more  or  less  all  the  others. 

The  flanks  are  arranged  to  cross  their  fires  in  front 
of  the  salients,  and  to  remove  the  dead  spaces  in  the 
ditches  (Fig.  9).  To  remove  the  dead  space  in  the 
ditch  in  front  of  the  curtain,  requires  that  the  fires 
from  the  flanks  should  reach  the  bottom  of  the  ditch 
at  the  middle  point  of  the  curtain.  To  cross  the 
fires  effectively  in  front  of  the  salients,  requires  that  the 
line  of  defence  should  not  be  longer  than  the  close 
and  effective  range  of  the  weapon  used  to  arm  the  flanks. 

It  is  plain  that  the  length  of  the  exterior  side 
must  depend  directly  upon  the  length  of  this  line  of 
defence,  and  that  the  length  of  the  curtain,  which 
must  admit  of  the  ditch  being  flanked,  must  depend 
upon  the  relief  of  the  interior  crest  of  the  flanks,  and 
the  inclination  of  the  superior  slope. 

The  shorter  the  line  of  defence  can  be  made,  at 
the  same  time  keeping  the  curtain  long  enough  to  al- 
low its  ditch  to  be   swept   by   the   fire  of    the   flanks. 


FIELD    WORKS,  51 

the  more  effective  will  be  the  cross  fires  in  front  of 
the  salients,  the  longer  will  the  enemy  be  under 
this  cross  fire,  and  the  greater  will  be  the  chances 
of  repulsing  any  assault  made  by  him. 

51.  Least  and  greatest  exterior  sides  of  a 
bastioned  front. — Taking  the  height  of  parajoet  at 
eight  feet  and  the  depth  of  the  ditch  at  six  feet,  this 
relief  of  fourteen  feet  will  be  the  least  used ;  tak- 
ing the  height  at  twelve  feet,  and  the  depth  at 
twelve,  the  corresponding  relief  of  twenty-four  feet 
will  be  the  greatest  used. 

Assuming  the  superior  slope  at  \,  the  least  length 
of  curtain  for  the  least  relief  is  fifty-six  yards  ;  the 
least  length  for  the  greatest  relief  is  ninety-six  yards. 

Using  the  construction  given  in  Art.  57,  it  will 
be  seen  that  for  a  curtain  of  fifty-six  yards  in  length, 
the  exterior  side  must  be  about  125  yards  long ;  for 
the  curtain  of  ninety-six  yards,  the  exterior  side  must 
be  two  hundred  and  fifty  yards  long. 

The  least  length  of  the  exterior  side  will  there- 
fore be  between  one  hundred  and  twenty-five,  and 
two  hundred  and  fifty  yards,  depending  upon  the  re- 
lief of  the   work. 

The  greatest  length  of  the  exterior  side  depends 
upon  the  length  given  to  the  line  of  defence.  If 
the  weapon  used  to  arm  the  flanks  is  the  rifled  mus- 
ket— the  weapon  now  used  by  infantry — its  close  and 
efl'ective  range  determines   the  length  of   the   line   of 


5/5  FIELD  FORTIFICATIONS. 

defence.  The  limit  of  accurate  aim  for  the  ordinary 
soldier  is  about  three  hundred  yards.  Assuming  this 
to  be  the  length  of  the  line  of  defence,  the  exterior 
side  will  be  about  four  hundred  yards  long,  and  will 
be  the  greatest  length  ordinarily  used. 

52.  Defects  of  a  bastioned  fort. — The  bas- 
tioned  fort  can  not  be  used  upon  an  irregular  site, 
without  sacrificing  some  of  its  most  important  quali- 
ties. It  requires,  also,  considerable  time  and  labor  to 
build  it. 

For  these  reasons  it  is  rarely  used  as  a  field 
work,  except  when  it  is  to  be  an  independent  work, 
and  used  to  defend  some  important  point. 

One  point  in  the  trace  of  the  bastioned  fort  re- 
quires particular  attention,  and  that  is  the  counter- 
scarp of  the  ditch.  If  the  counterscarp  is  kept  par- 
allel to  the  interior  crest,  there  will  be  a  dead 
space  in  the  ditch  near  the  shoulder  angle,  and  in 
the  ditches  in  front  of  the  flanks,  unless  a  modi- 
fication is  made  either  in  the  profile  or  in  the  width 
of  the  ditch. 

The  modifications  usually  made  are  of  three  kinds, 
and  are  as  follows  : 

One  is  to  widen  the  ditch  in  front  of  the  curtain 
by  removing  all  the  earth  included  between  the  cur- 
tain, the  flanks,  and  the  counterscarps  of  the  faces 
prolonged.  This  method  removes  the  dead  space  en- 
tirely. 


FIELD    WORKS,  53 

Another  is  to  widen  the  ditch  at  the  top  only, 
by  giving  the  counterscarp  of  the  ditch  in  front  of 
the  flanks  and  on  the  prolongation  of  the  faces,  a  slope 
which  will  expose  the  bottom  of  the  ditch  in  front  of 
the  flanks  to  the  fire  from  the  flank  opposite.  This 
method  removes  the  dead  space. 

A  third  way  is  to  slope  the  counterscarp  of  the 
prolongation  of  the  ditch  in  front  of  the  faces,  so  that 
the  bottom  of  this  ditch  in  front  of  the  shoulder 
angles  shall  be  swept  by  the  fire  of  the  flanks.  This 
method  removes  the  dead  space  in  the  ditches  of  the 
faces,  but  does  not  remove  those  of  the  flanks. 

The  first  method  is  the  one  used  in  permanent 
fortifications.  The  amount  of  time  and  labor  required 
to  make  this  modification  forbids  its  use  in  field 
works. 

The  second  method  has  the  same  defects,  but  not  to 
so  great  a  degree. 

The  third  method,  though  partial  in  it  effect,  is 
the  one  generally  adopted  in  field-fortifications. 

53.  Defects  of  the  star  fort, — Star  forts  are 
better  adapted  to  irregular  ground  than  the  bastioned 
forts.  Otherwise,  they  possess  all  the  defects  of  the 
latter,  without  the  complete  flanking  arrangements 
which  characterize  the  bastioned  system. 


CHAPTER    VI. 

LINES. 

54.  Classes  of  lines. — The  field  works  known  as 
lines  are  divided  into  classes,  according  to  the  object 
for  which  they  are  constructed  ;  or,  according  to  some 
peculiar  arrangement  of  their  parts,  or  other  charac- 
teristic quality.  Some  of  the  most  commonly  known 
are  the  lines  of  circumvallation ;  of  counter- 
vallation ;  intrenched  camps ;  single  and 
multiple  lines ;  continued  lines  •  lines  "with 
intervals;   etc. 

The  classification  of  lines  into  continued  lines  and 
lines  with  intervals  is  the  one  which  is  used  in  this 
chapter. 

55.  Continued  lines. —  When  the  entire  front 
to  be  defended  is  covered  by  a  continuous  line  of  para- 
pet, the  work  is  called  a  continued  line.  There  are 
no  openings  in  a  continued  line,  except  those  made  for 
the  use  of  the  defence. 

56.  Lines  with  intervals. — When  the  front 
to  be  defended  is  covered  by  a  number  of  field  works, 
scattered  along  this  front,  and  placed  near  enough  to- 
gether, to  sweep  the  intervals  with  their  fire,  the 
whole  arrangement  forms  a   disposition  called    a  line 


LINES. 


55 


•with  intervals. — Field  works  placed  so  near  to 
each  other,  that  each  one  can  bring  its  fire  to  bear 
upon  the  ground  in  front  of  those  adjacent,  are  said 
to  be  in  defensive  relations  witli  each  other. 

I.    Continued  Lines. 

57,  Kinds  of  continued  lines. — The  principal 
types  of  continued  lines  in  use  are  the  straight  line, 
the  tenaille  line,  the  redan,  the   indented,  and 

the  bastioned  lines,  which  are  easily  distinguished 
from  each  other  by  their  traces. 

58.  Tenaille  line.  The  trace  of  the  tenaille 
line  is  formed  by  making  the  alternate  angles  salient 
and  re-entering ;  the  condition  being  imposed  that  the 


H  D  6 


re-entering   angles  must   not   be   less    than    90%   nor 
greater  than  120°  (Fig.  10). 

The  line  A  B,  joining  the  extreme  right  and  left 


Oti  FIEJsD   FORTIFICATION  Hi, 

salients,  is  called  the  front ;  and  the  ground  in  front 
of  it,  within  range  of  the  fire  from  the  line,  is  called 
the  zone  of  defence. 

The  greatest  length  of  the  faces  depends  upon  the 
range  of  the  weapon  used  in  its  defence.  The  main 
object  of  the  tenaille  line  is  to  obtain  a  cross  fire  upon 
the  zone  of  defence.  This  cross  fire,  to  be  effective, 
must  be  within  the  range  of  accurate  aim  of  the  wea- 
pon used. 

To  find  the  greatest  length  for  the  faces,  the  fol- 
lowing construction  may  be  used.  Assume  the  angles 
for  the  salients,  which  must  be  known.  Take  the 
salient  at  A?  and  produce  the  face  F  A,  until  the  dis- 
tance A  Pj  is  equal  in  length  to  the  range  assumed. 
Through  this  point,  R,  draw  a  line  R  C  parallel  to  the 
capital  A  Hj  and  produce  it  until  it  intersects  A  B?  the 
front  of  the  line.  Its  point  of  intersection  with  this 
line  will  determine  the  position  of  the  salient  adjacent 
to  A-  Since  the  re-entering  angle  is  not  to  be  less  than 
90°,  the  greatest  length  of  the  faces,  when  the  positions 
of  the  salients  are  fixed,  will  be  when  the  re-entering 
angle  is  90°.  For  angles  greater  the  length  of  the 
faces  will  be  less. 

The  least  length  of  face  is  taken  at  thirt}^  yards, 
so  that  there  shall  be  no  dead  spaces  in  the  ditch  at 
and  near  the  salients. 

The  more  obtuse  the  salient  angles  are  made, 
the  more  difficult  it  will  be  for  the  enemy  to  enfilade 


LINES,  57 

the  faces.  This  exposure  to  enfilading  fire,  and  the 
amount  of  labor  required  to  construct  the  line,  are  the 
principal  objections  to  its  use. 

59.  Redan  line. — A  series  of  redans,  placed  at 
intervals  and  connected  by  straight  lines  of  parapet, 
(Fig.  11)  or  by  lines  with  very  slight  re-entrants,  or 
salients,  is  termed  a  redan  line. 


Fig.  11. 


The  traces  of  the  redans  are  usually  made  equila- 
teral triangles.  The  salients  are  placed  about  two 
hundred  and  forty  yards  apart,  and  the  faces  are 
made  sixty  yards  long.  This  line  is  sometimes  known 
as  Vauban's  line. 

There  is  another  redan  line  composed  of  large 
and  small  redans,   like  that  shown  in  Fig.   12.     It  is 

Fig.  12. 


known  as  a  continued  redan  line,  to  distinguish  it 
from  Vauban's  line. 

60.  Indented  lines. — The  indented,  or  cr^- 
maill^re  line  consists  of  short  and  long  branches, 
which  may  be  arranged  as  represented  in  Fig.  13. 

The  long  branches  are  usually  made  seventy  yards 
long,  or  more,  and  are  directed  towards  ground  which 


58 


FIELD  FORTIFICATIONS. 


cannot  be  occupied  by  an  enemy.     The  short  branches 
are   made   about   thirty  yards  long,    and    are   used  to 

Fig.  13. 


flank  the  long  branches.  Instead  of  giving  the  long 
branches  directions  parallel  to  each  other,  as  indicated 
in  Fig.  13,  they  may  all  be  directed  upon  a  single 
point,  which  the  enemy  cannot  reach,  as  shawn  in 
Fig.  14. 

Fig.  14. 


61.  Bastioned  line.  A  bastioned  line  is  com- 
posed of  a  series  of  bastioned  fronts,  joined  to  each 
other  on  the  same  general  line,   (Fig.  15)  the  salients 

Fig.  15.  • 


being  placed  from  two  hundred  and  fifty  to  four  hun- 
dred yards  apart.  The  line  joining  any  two  consecu- 
tive salients  is  taken  as  an  exterior  side,  and  a  bas- 
tioned front  constructed  upon  it  by  the  rules  already 
given. 

62.  Advantages  and  disadvantages  of  con- 
tinued   lines. — Continued     lines    have    been    much 


LINES,  59 

used  in  past  military  operations,  and  will,  in  all  prob- 
ability, be  used  in  the  operations  of  the  future. 

Continued  lines  may  be  usefully  employed  where 
a  passive  defence  only  is  to  be  made,  and  where  the 
position  to  be  defended  is  limited  in  extent,  and  not 
exposed  to  flank  attacks. 

They  are  not  fitted  for  an  active  defence,  and  they 
have  the  serious  disadvantage  of  being  untenable,  when 
any  part  of  the  line  has  been  taken  by  the  enemy. 

They  require  a  large  amount  of  labor  to  construct ; 
and  it  is  a  very  doubtful  question,  whether  the  ad- 
vantages they  give  compensate  for  the  time  and  labor 
employed  in  their  construction. 

II.  Lines  with  Intervals. 

63.  Lines  with  intervals. — This  class  of  lines 
differs  from  the  continued  lines, .  by  leaving  intervals 
along  the  front  of  the  position  which  intervals  pre- 
sent no  obstructions  to  an  enemy  moving  through 
them,  excepting  so  far  as  they  may  be  defended  by 
the  fire  of  the  works,  or  may  be  obstructed  by  natural 
obstacles,  or  by  artificial  ones  placed  along  the  front. 

The  works  forming  the  line  may  be  placed  so  close 
to  each  other,  as  to  be  in  defensive  relations;  or  they 
may  \)e  so  far  apart,  as  to  admit  only  of  their  de- 
fending the  intervals  between  them. 

If  the.  works  forming  the  line  are  to  be  in  defen- 
sive relations,  that  is,  if  they  are  to  aiford  a  reciprocal 


60  FIELD   FORTIFICATIONS, 

defence,  it  is  evident  that  the  remarks  made  upon 
obtaining  the  length  of  the  line  of  defence,  in  a 
flanked  disposition,  apply  equally  to  determining  the 
distance  between  the  works.  Thus,  a  line  of  redoubts 
(Fig.  16)  placed  so    that  their  salients  are  three  hun- 


dred yards  apart,  along  the  line,  A  B?  would  have  the 
works-  on  this  line  in  defensive  relations  with  each 
other,   the  weapon  used  being  the  musket. 

If  it  be  required  to  defend  only  the  intervals  be- 
tween them  with  the  musketry  fire,  this  distance  be- 
tween the  salients  of  the  consecutive  works  might  be 
as  much  as  six  hundred  yards,  as  this  would  bring 
the  middle  portion  of  the  interval  within  the  range 
of  accurate  aim. 

If  the  defence  is  to  be  made  with  artillery,  the 
distance,  in  the  first  case,  might  be  one  thousand,  or 
even  so  great  as  one  thousand  five  hundred,  yards. 
In  the  second  case,  these  distances  may  be  doubled. 

If  an  obstinate  defence  is  to  be  made,  a  second 
line  should  be  used  (Fig.  16).  A  second  line  is  es- 
pecially useful  when  the  works  on  the  outer  line  are 
not  in  defensive  relations  with  each  other. 


LINES, 


61 


The  second  line  should  be  placed  behind  the 
first,  and  distant  from  it,  about  one-fourth,  and  cer- 
tainly not  greater  than  one- half,  of  the  distance  be- 
tween the  works  in  the  first  line.  When  artillery 
is  used  in  the  second  line,  a  good  position  would  be 
about  six  hundred  yards  distant  from  the  first.  This 
places  the  second  line  just  out  of  range  of  aimed 
musketry  fire,  but  in  close  range  of  artillery  fire. 

64.  A  third  line  of  field  works  is  sometimes 
built.  The  general  arrangement  of  the  works  of  this 
third  line,  with  the  works  of  the  first  and  second, 
conforms  to  the  principles  employed  in  arranging 
the  works  in  the  second  line  (Fig.  17). 


A  third  line  might  be  useful,  in  case  of  an  active 
defence,  since  the  works  placed  along  this  line  can  be 
utilized  as  screens  for  the  reserves  and  for  bodies  of 
cavalry. 

A  fourth  line  would  evidently  be  of  no  practical 
service  in  the  defence  of  a  position.     A  force,  unable 


6i2  FIELD  FORTIFICATIONS. 

to  retain   possession  of  the  outer  lines,  could  not  be 
expected  to  hold  the  fourth. 

The  number  of  lines,  whether  a  single  one,  or  two, 
or  three  in  number  ;  the  kinds  of  works  to  be  used 
on  each  line ;  the  distance  apart  of  the  works  on  each 
line ;  the  distance  apart  of  the  lines ;  and  the  details 
of  their  construction,  depend  upon  the  natural  fea- 
tures of  the  ground,  the  numbers  and  kinds  of  troops 
which  are  to  occupy  them,  the  range  of  the  arm  used 
in  their  defence,  and  the  time  disposable  in  which  to 
construct  them. 

65.  Advantages  and  defects  of  lines  vrith 
intervals. — Certain  advantages  are  claimed  for  lines 
with  intervals.  These  advantages  may  be  briefly  stated 
to  be  as  follows  : 

1.  The  lines  with  intervals  admit  of  either  passive 
or  active  defence.  They  are  peculiarly  fitted  for  the 
latter. 

2.  Lines  with  intervals  are  more  easily  adapted  to 
the  natural  features  of  the  ground  than  continued  lines. 

3.  For  the  same  extent  of  front,  they  require  fewer 
men  to  defend  them,  and  the  works  require  less  labor 
to  construct,  than  other  kinds  of  lines. 

4.  They  admit  of  a  better  use  being  made  of  raw 
and  inexperienced  troops. 

5.  A  line  with  intervals  may  still  be  defended,  even 
after  a  part  of  the  line  has  been  captured,  or  after  the 
enemy  has  broken  through  the  line. 


LINES,  63 

The  main  defect  inherent  in  lines  of  this  class,  is 
the  sub-division  of  the  defenders  into  several  independ- 
ent commands,  by  which  unity  of  action  of  the  whole 
command  is  impaired. 

This  defect  is  reduced  somewhat  by  a  proper  dis- 
position of  the  works.  A  few  capacious  and  strong 
works  are  better  than  a  large  number  of  small  ones. 
Experience  has  shown  that  a  body  of  one  thousand 
men,  in  a  single  well-constructed  work  will  offer  a  more 
effective  resistance  to  the  attacks  of  an  enemy  than  the 
same  number  would,  when  scattered  among  three,  four, 
or  more,  smaller  works.  The  difficulty  which  a  gen- 
eral would  meet,  in  obtaining  experienced  officers  fit 
for  these  independent  commands,  and  in  having  these 
officers  to  act  in  unison  with  each  other,  gives  sufficient 
grounds  for  such  a  result  to  be  expected  under  ordin- 
ary circumstances. 


CHAPTEE    VII. 

THE     SIZE     OF     A     FIELD   WORK,    THE    NUMBER   OF    THE 
GARRISON,    AND   THE   SELECTION   OF   A   TRACE. 

66.  Size. — The  size  of  a  field  work,  when  built 
upon  a  level  site,  depends  principally  upon  the  number 
of  men  intended  for  its  defence.  When  built  upon 
an  irregular  site,  the  size,  in  addition,  depends  fre- 
quently upon  the  extent  of  ground  to  be  swept  by  the 
fire  of  the  work. 

A  good  defence  of  a  work  is  obtained  only  by  a 
strong  musketry  fire,  which  is  only  obtained  by  allow- 
ing a  musket  for  each  pace,  measured  on  the  interior 
crest.  The  number  of  men  to  form  a  single  rank  and 
to  furnish  this  fire  would  be  equal  to  the  number  of 
paces  contained  in  the  length  of  the  interior  crest. 

It  will  be  sufficiently  accurate  to  assume  four  paces 
for  each  three  yards  in  length.  An  interior  crest  of 
three  hundred  yards  would  require  four  hundred  men 
to  line  it  in  single  rank. 

A  vigorous  defence  requires  not  only  men  enough  to 
line  the  parapet,  but  a  good  many  more  to  supply  the 
vacancies  from  casualties  or  other  causes,  and  to  furnish 
support  to  the  line.  Double  the  number  required  to 
man  the  parapet  is  considered  to  be  sufficient.      That 


THE  ISIZE    OF  A    FIELD    WORK,  65 

is,  a  vigorous  defence  of  three,  hundred  yards  of  inte- 
rior crest  would  require  a  total  of  eight  hundred  men. 

Hence,  to  determine  what  the  length  of  interior 
crest  shall  be,  the  number  of  men  being  known,  it  will 
only  be  necessary  to  divide  the  number  of  men  by  two, 
and  take  this  quotient  for  the  number  of  paces  which 
the  interior  crest  should  have. 

Conversely,  the  length  of  interior  crest  being 
known,  it  will  only  be  necessary  to  find  the  number 
of  paces  in  its  length,  and  double  this  number  for 
the  number  of  men  which  will  be  required. 

67.  Grarrison. — A  body  of  troops  stationed  in 
or  near  a  field  work,  to  defend  it,  is  called  its  garri- 
son. 

The  garrison  of  a  work,  when  it  is  practicable, 
should  always  be  a  complete  organization,  or  composed 
of  detachments  belonging  to  the  same  unit  of  force. 

Garrisons  should  not  live  within  field  works,  un- 
less there  is  a  pressing  necessity  for  this  to  be  done. 
As  a  rule,  they  should  encamp  near  the  works  they 
are  to  defend,  and  only  keep  guards  within  the 
works. 

Nevertheless  the  engineer,  or  other  officer,  who 
lays  out  a  field  work  should  always  consider  the  pos- 
sibility of  its  being  occupied  by  a  garrison,  and 
should  provide  the  necessary  accommodations,  so  far 
as  interior  space  may  be  required. 

The   amount   of    interior  space  to   be  enclosed  be- 


66  FIELD  FORTIFICATIONS. 

comes  a  matter  of  importance  under  these  circum- 
stances, and  especially   in  redoubts. 

68.  Enclosed  space. — The  amount  of  space  to 
be  enclosed  by  a  redoubt  can   be  easily  calculated. 

It  is  usual  to  allow  from  one  and  a  half  to  two 
square  yards  of  space  for  each  man  ;  a  space  of  sev- 
enty-five square  yards  for  each  field  gun  ;  a  space  of 
twenty  square  yards  for  a  powder  magazine ;  and  a 
space  of  one  hundred  and  seventy-five  square  yards 
for  a  traverse  which  is  used  to  protect  the  outlet, 
or  passage  way,  leading  out  of  the  work. 

Suppose  a  field  work  is  to  be  built,  which  is  to 
be  a  square  redoubt,  to  be  armed  by  four  field  guns, 
and  to  have  a  traverse  opposite  the  outlet ;  what  is 
the  area  to  be  enclosed,  and  the  length  of  interior 
crest,  the  garrison  numbering  four  hundred  men  ? 

From  the  quantities  above,  the  space  for  the  ac- 
commodation of  the  men,  etc.,  will  be  as  follows  : 

400  men,  allowed  2  square  yards  each,  800  square  yards. 
4  field  guns,  ''  75     ''         "         "      300      " 
1  powder  magazine,  20      '^        " 

1  traverse,  175      '' 

Total    1295      " 

In  addition  to  this  space,  there  must  be  room  for 
the  part  of  the  parapet  between  the  interior  crest  and 
the   banquette  slope.     The   distance  from   the  foot  of 


THE  SIZE   OF  A   FIELD    WORK,  G7 

the  banquette  slope  to  the  sub-crest,  in  the  ordi- 
nary profile,  is  three  yards.  This  distance  must  be 
enclosed,  as  necessary  for  the  troops. 

The  square  root  of  1295  may  be  taken  to  be 
thirty-six. 

A  square  whose  sides  are  each  thirty-six  yards 
long  will  enclose  a  space  sufficient  for  the  accommo- 
dation of  the  men  and  guns,  and  allow  for  a  traverse 
and  a  magazine.  If  a  square  be  taken  whose  sides 
are  six  yards  longer,  that  is,  each  side  equal  to  forty- 
two  yards  in  length,  it  will  enclose  a  space  sufficient 
for  the  men,  guns,  etc.  ;  and  will  also  allow  room  for 
the  parapet. 

A  square  redoubt  whose  sides  are  forty-two  yards 
long,  or  whose  entire  interior  crest  is  one  hundred  and 
sixty-eight  yards  long,  will  enclose  space  enough  to 
accommodate  a  garrison  of  four  hundred  men,  four 
guns,  etc. 

The  rule  given  in  Art.  ^Q,  would  require  a  force 
of  four  hundred  and  forty-eight  men  to  defend  this 
work.  It  is  evident,  then,  that  there  must  be  a  least 
length  of  interior  crest,  which  being  defended  accord- 
ing to  the  rules  laid  down,  shall  enclose  the  necessary 
space  for  the  accomodation  of  the  garrison. 

69.  Relation  between  least  length  of 
interior  crest  and  space  enclosed  for  a 
square  redoubt  for  a  given  number  of  men, 
etc. 


68  FIELD    F01^TJFICATI02\S. 

Let  X  represent  the  number  of  yards  in  the  interior 
crest  of  one  of  the  sides  of  the  redoubt ; 

n,    the   number    of    men    forming    the    garrison ; 

s',  the  number  of  square  yards  allowed  for  the 
guns,  magazine,   and  traverse. 

Let  it  be  supposed  that  each  man  is  allowed  two 
square  yards,  and  that  for  every  three  yards  of  interior 
crest,  there  shall  be  eight  men. 

These  conditions  may  be  expressed  by  the  follow- 
ing equations. 

(a;-6)«  =  2n-h  s' (1) 

in  =  ix  X  A (2) 

If  the  redoubt  is  to  be  armed  with  field  guns,  and 
to  have  a  powder  magazine  and  a  traverse,  the  value 
of  s'  may  be  determined  by  the  rule  already  given. 

Suppose  the  redoubt  is  to  be  armed  with  four 
field  guns,  etc.,  and  that  the  space  allowed  for  them 
is  that  named  in  the  last  article.  After  substituting 
for  s,  its  value,  four  hundred  and  ninety-five  square 
yai'ds,  equations  (1)  and  (2)  may  then  be  combined 
and  solved  with  respect  to  x  and  n.  Their  values 
will  be  found  to  be 

X   =    44,         and         7i    ~   473. 

If  tlie  redoubt  is  not  to  be  armed  with  artillery, 
but  is  to  have  a  traverse  opposite  the  outlet,  the 
value   of    6*'    will    be    one    hundred     and    seventv-five 


SELECTION   OF  THE    TRACE. 


C9 


yards,    and   the    corresponding   rallies  for    x   and    n, 
will  be 

X   —    37,        and        n   =   395. 

All  square  redoubts  in  which  the  lengths  of  the 
sides  are  less  than  thirty-seven  yards  and  forty-four 
yards,  will  not  have  the  requisite  space  enclosed. 
Since  the  area  increases  in  a  much  more  rapid  ratio 
than  the  perimeter,  all  square  redoubts  whose  sides 
are  longer  than  those  named,  will  contain  more  space 
than  is  absolutely  sufficient. 

70.  Selection  of  the  trace.  The  selection  of 
the  trace  of  a  field  work  is  dependent  upon  the  num- 
ber of  men  that  can  be  spared  to  defend  it,  and  upon 
the  time  that  can  be  allowed  in  which  to  build  it. 

The  selection  is  also  dependent  upon  the  natural 
features  of  the  site.  Thus,  suppose  a  field  work  is  to 
be  placed  in  front  of  a  bridge,  to  defend  the  crossing 
of  the  river  at   that  point   (Figs.    18  and  19).      The 


Fig.  18. 


Fig.  19. 


redan,  which   was  a  fitting  trace  where  its    site  is  in 
the  bend  of  the  river  (Fig.  18)    would  not  be  so  well 
fitted  for  the   defence  as  a  lunette   would   be,  if   the 
site  is  bounded  by  a  straight  course  of  river  (Fig.  19.) 
The  selection  is  also  influenced  by  the  particular 


70  FIELD  FORTIFICATIONS, 

object  to  be  attained.  It  is  plain  that  a  trace  which 
would  bring  a  strong  direct  fire  upon  ground  which 
an  enemy  would  not  occupy,  would  be  a  faulty  one. 
The  arrangement  of  the  trace  upon  the  site,  after 
the  trace  has  been  chosen,  is  an  important  matter,  and 
may  be  considered  as  a  part  of  the  selection. 

Thus,  a  field  work  to  be  built  in  rear  of  a  marsh, 
the  crossing  of  which  is  impracticable  for  the  enemy 
(Fig.   20)  would  have  a  faulty  trace,  if  its  lines  were 

Fig.  20.  ^         .-i^j:^-^ 


H 


60  placed  as  to  bring  strong  direct  fires  upon  the 
marshy  ground,  and  not  upon  those  portions  along 
which  the  enemy  would  be  obliged  to  approach  in 
his  advance  upon  the  work. 

The  same  fault  would  exist  where  the  trace  was 
assumed,  if  its  lines  were  not  properly  directed.  Thus, 
suppose  a  square  redoubt  was  to  be  placed  in  rear  of 
the  marsh,  it  is  plain  that  the  redoubt  B  (^ig-  ^0) 
would  have  the  defect  just  named,  while  the  redoubt  A 
would  not. 

If,  instead  of  a  marsh,  the  ground  had  been  high. 


SELECTION  OF   THE   TRACE,  71 

it  is  easily  seen  that  the  redoubt  at  A  is  better  placed 
than  the  one  at  Bi 

No  absolute  rules  can  be  laid  down  which  will  apply 
to  all  cases.  The  engineer  must  exercise  his  skill  and 
ingenuity  in  each  case,  taking  care  to  harmonize  as  far 
as  possible  the  conditions  to  be  observed,  whenever  they 
conflict. 


CHAPTER  VIII. 

CONSTRUCTIOiq"   OF   FIELD   WORKS. 

71.  Tracing. — After  having  determined  upon  the 
dimensions  of  the  profile,  and  having  selected  the  trace, 
the  first  step  in  building  the  work  is  to  mark  its  out- 
line ]ipon  the  ground.  This  operation  is  called  trac- 
ing. The  operation  of  tracing  consists  in  marking  the 
sub-crest  and  other  necessary  lines  upon  the  ground, 
so  that  they  can  be  distinctly  seen,  and  can  be  used 
to  determine  all  other  lines  and  points  of  the  work. 

The  ^^  tracing'^  of  a  field  work  may  be  made  by 
means  of  a  drawing  which  represents  the  work  to  be 
constructed  ;  or  it  may  be  made  directly  upon  tlie 
ground  without  the  use  of  a  drawing. 

When  a  drawing  is  used,  it  is  usual  to  take  two 
points  upon  this  drawing,  which  can  be  easily  located 
upon  the  ground,  and  join  these  points  by  a  straight 
line.  This  line  is  then  taken  to  represent  a  base  line 
which  can  be  used  in  laying  out  the  work.  From 
the  different  angular  and  important  points  of  the 
plan,  perpendicular  lines  are  drawn  to  this  base  line. 
The  distances  to  the  base  line,  and  the  distances  in- 
tercepted upon  it,  are  measured  and  noted  upon  the 
drawing.     Going  to  the  site,    the  two   assumed  points 


CONSTRUCTION  OF  FIELD    WORKS,  73 

are  located  upon  the  ground,  and  a  straight  line  is 
drawn  through  them.  This  line  is  the  base,  and  is 
marked  upon  the  ground  either  by  a  cord,  or  by  a 
furrow  in  the  ground  made  with  a  pick.  The  distances 
are  then  measured  o&.  on  the  base  line,  and  the 
points  marked  where  the  perpendiculars  are  to  be  con- 
structed. These  perpendiculars  are  then  constructed 
by  some  of  the  simple  methods  used  for  this  purpose, 
and  the  distances  to  the  angular  points  laid  off  on 
these.  These  points,  thus  determined,  are  then 
marked  by  stout  pickets  driven  into  the  ground. 
The  angular  points  are  then  joined  by  straight  lines, 
and  these  lines  are  then  marked  upon  the  ground  by 
a  cord  stretched  between  the  adjacent  j^oints,  or  by  a 
furrow  made  in  the  ground.  The  marking  of  these 
lines  completes  the  tracing  of  the   sub-crest. 

If  there  is  no  drawing,  but  the  work  is  to  be  laid 
out  directly  upon  the  ground  chosen,  it  is  usual  for 
the  engineer  to  first  select  the  salient  points  of  the 
work,  and  mark  them  by  stout  pickets  driven  into 
the  ground.  He  may  then  determine  the  reentrants 
by  inspection,  or  by  some  rule.  Which  method  he 
will  use  will  depend  upon  the  kind  of  tracing  to  be 
made.  The  angular  points,  all  determined,  are  then 
connected  by  straight  lines,  marked  as  in  the  previous 
case. 

72.  Profiling. — The  operation  called  profiling 
forms  the  next  step  in  the  construction.     This  opera- 


74 


FIELD   FORTIFICATIONS. 


tion  consists  in  erecting,  at  proper  points  along  the  sub- 
crest,  wooden  profiles  which  give  the  form  of  the 
parapet  at  those  points,  and  which  guide  the  workmen 
in  the  construction  of  the  work. 

Profiles  are  placed  at  the  extremities  of  a  parapet ; 
at  points  along  the  sub-crest  from  twenty  to  thirty  yards 
apart ;  at  the  salients  and  reentrants  ;  and  at  any  points 
where  a  change  is  to  be  made  in  the  dimensions,  or  in 
the  direction  of  the  parapet.  The  profiles  are  made 
perpendicular  to  the  subcrest,  excepting  at  the  angles, 
where  they  are  made  to  bisect  the  angles. 

An  ordinary  profile  may  be  constructed  as  follows  : 
A  straight  line,   as   D'  K   (Fig.  21.)  is  drawn  on  the 

Fig.  21. 


ground  at  D  ^^^^  perpendicular  to  the  sub-crest.  A 
distance,  D'  E'?  equal  to  the  thickness  of  the  parapet, 
is  laid  off  and  marked  by  stout  pickets  driven  into 
the  ground,  at  D'  and  £'•  Poles  or  strips  are  nailed 
to  these  pickets  in  a  vertical  position,  and  held  firmly 
in  place  by  a  strip,  H  H  ?  fastened  to  them.  It  will  be 
found  convenient  to  make  this  strip  horizontal,  which 
may  be  done  by  a  level. 


CONSTRUCTION  OF  FIELD    WORKS.  75 

The  height  of  the  interior  crest  is  marked  on  the 
pole  at  D'?  and  the  exterior  crest  on  that  at  £'.  A 
wooden  strip,  from  two  to  three  inches  wide,  and  one 
inch  thick,  is  then  nailed  to  these  poles  at  the  points 
D  and  E,  just  marked.  These  wooden  strips  may  be 
made  by  sawing  boards  into  pieces  of  the  necessary 
width. 

A  distance  H"  F  is  laid  off  on  the  horizontal  strip 
H  H'^  equal  to  the  base  of  the  slope  which  the 
earth  is  to  take.  A  stake  is  driven  at  this  point,  and 
the  point  p  marked  upon  it.  A. strip,  E  f^  extended 
until  it  meets  the  ground,  is  then  nailed  to  the  up- 
rights, which  strip,  in  this  position,  marks  the  inclina- 
tion of  the  exterior  slope. 

Similar  strips  are  fastened  to  the  other  uprights  to 
mark  the  inclination  of  the  interior  slope,  the  width 
of  the  banquette,  and  the  inclination  of  the  banquette 
slope.  The  profiles  being  finished,  the  foot  of  the 
banquette  slope  and  the  foot  of  the  exterior  crest  are 
marked  upon  the  ground  in  a  way  similar  to  that 
used  for  the  sub-crest.  This  operation  completes  the 
profiling  and  tracing  of  the  parapet. 

The  profile  of  the  parapet  being  finished,  the 
points  G  and  K?  or  points  of  the  scarp  and  counter- 
scarp, are  marked  by  pickets  driven  into  the  ground. 
The  crests  of  the  scarp  and  counterscarp  are  then 
traced  upon  the  ground.  Where  attention  is  to  be 
paid  to  the  slopes  of  the  ditch,  short  strips  are  nailed  to 


76  FIELD  FORTIFICATIONS. 

the  pickets,  marking  the  inclinations  ^to  be  given.  In 
addition,  the  points  L  and  M  are  determined,  and  the 
lines  projected  in  these  points  are  traced  upon  the 
ground  by  means  of  a  pick. 

73.  Execution  of  the  work. — The  third  step 
is  begun  by  bringing  the  working  parties  on  the  ground 
and  commencing  the  excavation. 

The  first  thing  to  be  done  is  to  remove  all  brush, 
trees,  rocks,  or  obstructions,  which  may  hinder  the 
work  of  excavation. 

In  this  kind  of  work,  as  well  as  in  the  excavating, 
the  working  parties  are  divided  into  smaller  bodies, 
generally  termed  gangs. 

The  gangs,  being  furnished  with  shovels  and  pick- 
axes, are  distributed  along  the  line  of  the  ditch,  under 
the  supervison  of  competent  foremen. 

It  is  recommended  to  divide  the  crest  of  the  coun- 
terscarp into  lengths  of  six  feet  or  more  (sometimes 
twelve)  and  to  mark  the  divisions  by  small  pickets. 
The  sub-crest  is  then  divided  into  the  same  number 
of  divisions,  which  are  connected  with  those  already 
marked  upon  the  counterscarp,  by  furrows  traced  upon 
the  ground,  these  furrows  being  prolonged  until  they 
intersect  the  foot  of  the  banquette  slope.  In  this  way, 
there  are  formed  small  areas,  in  each  of  which  a  work- 
ing party  can  be  placed,  and  in  each  of  which  there 
will  be  room  for  the  party  to  work  without  crowding. 
The  number  of  workmen,  the  proportion  of  picks  and 


CONSTRUCTION  OF  FIELD    WORKS,  7? 

BhovelS;  and  the  positions  of  the  men,  will  depend  upon 
the  nature  of  the  ground  to  be  excavated  and  the  dis- 
tances to  which  the  earth  must  be  thrown. 

In  ordinary  soils,  one  man  with  a  pick  can  loosen, 
in  a  given  time,  as  much  earth  as  two  men  can  remove 
with  shovels,  during  that  time.  The  amount  of  earth 
removed  can  be  determined  experimentally,  by  having 
a  man  to  loosen  the  earth  over  a  given  space  to  the 
depth  of  one  blow  of  the  pick,  and  note  the  time 
employed.  Then  have  a  man  to  shovel  this  loosened 
earth  off,  and  throw  it  a  horizontal  distance  of  twelve 
feet,  and  note  the  time  taken  to  do  it.  With  the 
data  thus  obtained,  the  proportion  of  picks  to  shovels 
can  be  determined. 

It  is  assumed  that  a  workman  while  shovelling 
can  pitch  a  shovelful  of  earth  to  a  distance  of 
twelve  feet  in  a  horizontal  direction  or  of  six  feet 
in  a  vertical  one. 

The  shovellers  in  the  beginning  of  the  excavation 
can  therefore  be  placed  twelve  feet  apart ;  but  as  the 
ditch  deepens,  the  distance  apart  must  be  lessened, 
and  finally,  the  number  of  shovellers  must  be  in- 
creased. 

There  should  be  for  every  two  or  three  working 
parties,  one  man,  at  least,  to  spread  or  level  the  earth 
as  it  is  thrown  upon  the  embankment,  and  another 
man  to  ram  it. 

From  the  foregoing,  knowing  the  kind  of  soil  and 


78  FIELD  FORTIFICATIONS, 

the  dimensions  of  the  ditch  and  parapet,  the  size  of 
each  working  party  can  be  estimated. 

In  the  field,  the  workmen  are  soldiers,  taken  from 
infantry  regiments,  detailed  for  this  fatigue  duty 
The  details  are  divided  into  squads,  forming  working 
parties  under  the  supervision  of  their  non-commis- 
sioned officers.  Several  of  these  S(|uads  form  a  fa- 
tigue detail  under  the  charge  of  a  commissioned  offi- 
cer and  are  by  him,  divided  into  reliefs  according  to 
the  circumstances  of  the  case.  The  soldiers  are  dis- 
tributed, as  just  described,  along  the  line  of  the 
ditch,  excavating  the  earth,  throwing  it  upon  the 
embankment,  spreading  it,  and  ramming  it. 

There  should  be  present  with  every  fatigue  de- 
tail an  engineer  soldier,  who  should  explain  to  the 
men  their  duties,  before  they  begin  to  work  ;  should 
advise  them  how  to  ifSe  their  tools ;  and  should  be 
responsible  that  the  proper  slopes  and  dimensions  of 
the  profiles  are  observed. 

74.  Time  required. — The  day's  task  for  an  or- 
dinary workman  in  common  soil  is  about  eight  cubic 
yards,  when  the  earth  is  not  thrown  higher  than  six 
feet.  Half  of  this,  or  about  four  cubic  yards,  may 
be  taken  as  a  fair  day's  work  for  the  ordinary  soldier 
on  fatigue  duty,  if  he  works  faithfully.  The  time 
for  throwing  up  a  work,  whose  profile  is  that  shown 
in  fig.    (2),  may  be  roughly  calculated,   as  follows  : 

The  area  of  the  section   of  the  parapet  is   about 


CONSTRUCTION   OF  FIELD    WORKS.  79 

one  hundred  and  eighteen  square  feet.  The  area  laid 
off  for  a  working  party  has  a  length  of  six  feet.  It 
may  be  roughly  estimated  that  the  working  party 
assigned  to  one  of  these  areas  is  required  to  make 
an  embankment  containing  seven  hundred  and  eight 
cubic  feet,  or  about  twenty-six  cubic  yards.  An  ex- 
cavation which  measures  twenty- three  cubic  yards 
will  give  earth  enough  to  make  a  parapet  containing 
twenty-six  cubic  yards.  Calling  the  amount  of  exca- 
vation to  be  twenty-four  cubic  yards,  and  supposing 
each  party  to  take  out  only  four  cubic  yards  per  day, 
it  will  require  six  days   to   construct  the  parapet. 

The  parapet,  of  the  dimensions  given,  can  be  con- 
structed by  fatigue  details,  in  one-third  of  this  time,  or 
less,  by  increasing  the  number  of  men  in  each  work- 
ing party,  dividing  the  party  into  reliefs,  and  work- 
ing continuously  until  the  parapet  is  finished. 

When  the  embankment  has  reached  the  height  of 
the  banquette  tread,  additional  working  parties  are 
organized,  for  the  purpose  of  constructing  the  revet- 
ments, which  are  required  to  support  and  protect  the 
interior  slope. 

When  no  engineer  soldiers  can  be  spared  to  oversee 
the  work,  substitutes  must  be  obtained.  There  will 
be  found,  in  all  of  the  infantry  regiments  of  the  United 
States  service,  non-commissioned  officers  who  have  had 
experience  in  the  labors  of  excavating  and  embanking. 
These  can  be  detailed  to  act  as  engineer  soldiers  and 


80  FIELD  FORTIFICATIONS, 

* 

can  fit  themselves  in  a  very  short  time  to  discharge  the 
duties  assigned  to  them. 

The  method  of  posting  the  men  is  a  matter  of  detail, 
acquired  from  practice ;  the  only  condition  imposed  is 
that  there  shall  be  no  croioding.  Only  a  limited  num- 
ber of  men  can  work  at  the  same  time,  and  rapidity  of 
execution  can  only  be  obtained  by  frequent  reliefs. 
Eapidity  of  execution  is  facilitated  by  good  judgment, 
especially  in  the  selection  of  the  men.  Good  axemen 
should  not  be  used  to  dig ;  and  good  diggers  should 
not  be  used  as  axemen.  Proportioning  the  work  accord- 
ing to  the  skill  displayed  by  the  men  will  materially 
shorten  the  time  required  for  its  execution. 


CHAPTER    IX. 

REVETMENTS. 

75.  Definition. — Any  facing  used  to  protect  a 
slope  of  earth  from  the  action  of  the  weather  is  termed 
a  revetment.     (Art.  24.) 

Embankments  of  earth  are  frequently  made  with 
slopes  greater  than  the  one  which  the  earth  naturally 
assumes.  These  slopes,  when  left  exposed  to  the  action 
of  the  weather,  soon  wear  away  and  lessen  until  they 
coincide  with  the  natural  one.  Where  it  is  necessary 
to  preserve  them,  it  is  done  by  using  revetments,  or 
retaining  walls.  The  latter  are  necessary  when  there 
is  a  horizontal  thrust  due  to  a  mass  of  earth,  which 
would  fall  were  it  not  supported.  The  former  are  used 
where  there  is  little  or  no  thrust,  and  the  object  is 
principally  to  protect  the  slopes  from  the  weather. 

76.  Materials  used  for  revetments. — If 
there  is  time,  and  the  work  is  to  be  kept  in  good  con- 
dition, it  is  a  good  policy  to  protect  all  the  slopes,  by 
using  revetments,  or  by  sowing  the  slopes  with  grass 
seed. 

The  interior  slope  is,  however,  the  only  one  in   a 

field  work  that  requires  protection  as  soon  as  constructed. 

'  All  other  slopes   can   wait  until   the   parapet   is   com- 


82  FIELD   FORTIFICATIONS, 

pleted.  Field  works  are  frequently  constructed  hur- 
riedly, and,  in  consequence,  the  revetment  of  the  in- 
terior slope  must  be  made  quickly.  This  necessitates 
the  use  of  any  materials  suitable  for  the  purpose,  and 
which  can  be  quickly  procured.  Some  of  the  materials 
near  at  hand,  or  which  can  be  quickly  procured,  from 
w^hich  the  revetments  can  be  madC;  are  fascines, 
gabions,  hurdles,  timber,  plank,  casks  and 
barrels,   sandbags,  grass  sods,  etc. 

77.  Fascines. — A  fascine  is  a  long,  cylindrical, 
bundle  oi  brush-wood,  bound  closely  together  near  the 
ends  and  at  intermediate  points  by  withes  or  by  wire 
(Fig.  22). 

Fig.  22. 


A  fascine  is  usually  made  nine  inches  in  diameter, 
and  eighteen  feet  long.  The  method  of  making 
them  is  as  follows  :  Trestles  are  placed  in  line,  with 
the  end  ones  sixteen  feet  apart .  ^rtnuu^adiJorl^^Br.  If 
five  trestles  are  used,  the  trestles  would  be  four  feet 
apart.  Each  trestle  is  made  by  driving  two  stakes, 
each  six   and   a   half   feet   long,    and  three   inches    in 


REVETMENTS.  83 

diameter,  obliquely  into  the  ground  so  that  they  will 
nearly  make  a  right  angle  with  each  other,  and  bind- 
ing them  together  at  the  middle.  The  brushwood, 
stripped  of  its  leaves  and  small  twigs,  straight  and 
flexible,  and  about  an  inch  in  diameter,  is  laid  in  the 
trestles,  as  nearly  uniforiyily  in  thickness  as  possible, 
until  the  trestles  are  nearly  full. 

This  brushwood  is  compressed  into  a         p,-^^  23, 
compact  bundle  by  means  of  a  fascine   \\  /Y 

choker  (Fig.  23),  and  bound   firmly  by     \\  yV 

bands.  ##^p^^ 

The  fascine  choker  is  formed  of  two  \^H/ 
stout  levers,  which  are  connected  by  a 
piece  of  chain  or  stout  rope,  as  shown  in  the  fig- 
ure. Its  action  is  easily  understood.  The  bands 
are  usually  withes,  sometimes  called  gads,  pre- 
pared for  the  purpose.  The  bands  are  twelve  in 
number,  placed  at  equal  distances  apart ;  those  near 
the  ends  being  six  inches  from  the  end  of  the  fas- 
cine. Wire,  and  even  spun  yarn,  are  used  for  the 
bands  at  times. 

Every  third  or  fourth  band  should  be  made  with  a 
projecting  end,  terminating  in  a  loop.  This  loop  is  used 
to  go  around  a  small  picket  driven  into  the  earth, 
and  hold  the  fascine  in  its  place. 

After  practice,  a  fascine  can  be  made  by  a  squad 
of  five  men  in  about  an  hour. 

78.  Fascine  revetments. — The   revetment  of 


84  FIELD   FORTIFICATIONS. 

the    interior    slope,  by    using    fascines,  is    shown    in 
Fig.  24. 

Fig.  24. 


The  first  row  of  fascines  is  partly  imbedded  in 
the  earth,  so  that  about  half  of  the  thickness  of  a 
fascine  is  below  the  banquette  tread.  This  row  is 
held  firmly  in  place  by  small  pickets  driven  through 
the  fascine  and  into  the  earth  on  which  it  rests. 

The  other  rows  are  laid  on  top  of  the  first  row, 
and  on  each  other,  and  held  in  place  by  pickets ;  the 
fascines  in  each  row  breaking  joints  with  those  in 
the  row  beneath,  and  are  so  placed  as  to  have  a 
slope  of  f.  The  projecting  ends  of  the  bands  are 
stretched,  and  small  pickets  are  also  driven  through 
the  loops.  These  pickets  are  called  anchoring  pick- 
ets. Six  rows  of  fascines  would  place  the  top  of 
the  upper  row  within  four  inches  of  the  interior 
crest.  A  row  of  sods  should  be  laid  along  this  top 
row  to  complete  the  interior  slope. 

If  five  rows  only  are  used,  the  portion  of  the  in- 
terior slope  between  the  top  row  and  the  interior  crest 
is  left  to  stand  at  the  natural  slope  of  the  earth  until 


REVETMENTS.  85 

there  is  time  to  finish  it.      It  is   usually  finished  by 
means  of  sods. 

79.  Gabions.. — Gabions     are    basket-work    cylin- 
ders,  open  at  both  ends  (Fig.  25).     The  bas-     Fig.  25. 
ket-work  is  made  of  brushwood,  although  iron 
has  been  used. 

A  gabion  is    usually  made  two  feet  and 
nine  inches  high,  and  two  feet  in  diameter. 
The   method    used    ordinarily    in   making    a 
gabion  is  to  drive  pickets,    three  and  a   half 
feet    long,    into   the   ground    in    a    circular 
row.     The   size  of   the  circle  may  be  deter-    °o      ^o 
mined  by  a  circle  traced  on  the  ground,   or 
by  a  circular  piece  of  wood  called  a  gabion   form. 
The  gabion  form  is  then  raised  about  one  foot  above 
the  ground,  and  the  pickets  are  bound  firmly  together 
by  a  rope  passed  around  them  just  below  the  form. 

The  brush  wood,  stripped  of  leaves  and  twigs, 
straight  and  flexible,  and  about  one-half  inch  in  di- 
ameter, is  then  woven  around  the  pickets. 

The  most  approved  method  of  weaving  is  to  use 
thi-ee  rods  as  shown  in  Fig.  25.  The  three  rods  are 
placed  with  the  large  ends  inwards,  and  separated 
from  each  other  by  an  intervening  picket.  The  first 
rod  (the  one  in  rear)  is  passed  over  the  other  two 
rods,  around  two  pickets,  and  within  one  ;  the  second 
rod  (now  the  rear  one)  is  passed  over  the  rods,  around 
two  pickets,  and  within  one  ;  the  third  is  manipuhited 


86  FIELD    FORTTFI CATIONS. 

in  the  same  manner.  Each  rod  comes  to  the  front  in 
turn,  and  is  separated  from  the  others  by  a  picket. 
As  the  weaving  progresses,  the  basket-work  muse  be 
kept  pressed  down,  either  by  the  foot,  or  by  blows 
from  a  mallet  or  a  stout  stick.  When  the  basket- 
work  has  reached  the  height  of  two  feet  and  nine 
inches,  the  ends  of  the  rods  are  firmly  secured  by 
withes.  If  the  basket  work  is  not  of  the  requisite 
height,  by  reason  of  the  pickets  being  driven  too  far 
into  the  ground,  it  is  turned  over  and  added  to  on 
the  other  end,  both  ends  being  secured  by  withes. 
The  usual  number  of  pickets  is  nine,  but  a  larger 
number  may  be  used  when  the  brushwood  is  flexible 
and   small. 

With  a  form,  two  men  can  make  a  gabion  in  one 
hour  and  a  half;  without  it,  it  will  take  three  men 
about  two  hours  to  make  one  gabion. 

Gabion  revetments  are  rarely  used  for  the  interior 
slopes  of  ordinary  field  works.  They  are  much  and 
usefully  employed  in  the  trenches  in  siege  operations, 
in  batteries,  and  in  embrasures. 

When  used  as  a  revetment  for  the  interior  slope, 
they  give  a  height  of  three  feet,  in  consequence  of 
the  projecting  ends  of  the  pickets.  They  are  made 
to  rest  upon  a  row  of  fascines  half  buried  in  the  ban- 
quette, and  are  so  placed  as  to  have  the  same  inclina- 
tion as  the  interior  slope.  The  gabions  are  then  filled 
with   earth,   and   the   parapet  is   raised   behind    them. 


REVETMENTS.  87 

Wlien  the  parapet  reaches  the  height  of  the  gabion, 
a  row  of  fascines  is  laid  on  top  of  the  gabions  to  give 
tlie  requisite  height  to  the  interior  crest. 

80.  Hurdle  revetments. — Hurdle  revetments 
are  frequently  used  in  field  works. 

The  hurdle  is  ordinarily  two  feet  and  nine  inches 
high,  and  about  six  feet  long.  It  differs  in  construc- 
tion from  the  gabion,  only  in  having  the  pickets 
placed  in  a  straight  line,  or  along  a  line  which  is 
slightly  curved. 

When  used  for  revetting  long  lines  of  parapet,  the 
hurdles  are  made  continuous.  The  pickets  are  driven 
into  the  ground  as  close  to  the  parapet  as  possible,  leav- 
ing only  space  enough  to  allow  the  brushwood  being 
woven  in  and  out  and  around  the  pickets.  The  pick- 
ets should  have  the  same  inclination  as  that  of  the  in- 
terior slope,  and  be  tied  back  by  anchoring  pickets. 
A  larger  size  of  brushwood  can  be  used  for  this  revet- 
ment than  can  be  used  for  making  gabions. 

81.  Timber  Revetments. — Fascines,  gabions, 
and  hurdles  are  used  for  revetments  when  timber  is 
scarce,  or  there  are  better  uses  to  which  the  timber 
may  be  applied. 

Timber  is  a  suitable  material,  both  on  account  of 
its  comparative  durability,  and  for  the  ease  with  which 
it  can  be  worked  into  the  shapes  required.  Its  scarc- 
ity, and  its  usefulness  for  other  purposes,  are  the 
reasons   for  not    employing  it  more  freely   for    revet- 


H8  FIELD    FOirriFICATIOXS. 

ments.  When  abundant  it  will  be  used  in  preference  to 
any  of  the  other  materials  for  the  revetment  of  in- 
terior slopes  and  scarps. 

There  are  two  general  methods  employed  in  mak- 
ing timber  revetments.  One  method  is  to  place  the 
logs  in  a  horiisontal  position,  piling  them  in  rows 
one  above  the  other  with  the  proper  inclination,  and 
fastening  them  in  place,  by  pinning  the  layers  to- 
gether, and  by  anchoring  ties.  The  other  method  is 
to  cut  the  sticks  into  short  lengths  and  to  place  them 
in  contact  with  each  other  in  an  upright  position  ; 
then  cap  the  posts  by  a  horizontal  p*iece  of  timber. 
(Fig.  26.) 


Fig.  26, 


The  latter  method  is  considered  to  be  the  better 
one,  especially  in  the  event  of  a  cannon  shot  pene- 
trating the  parapet  and  striking  the  back  of  the 
revetment.  If  the  log  struck  is  knocked  out,  the 
sphere  of  injury  would  be  more  extended  when  the 
log  was  in  a  horizontal  position  than  if  it  were  in  an 
upright  one. 

This  method   of  revetting  the  slopes  (Fig.  26)  was 


REVETMENTS.  89 

much  used  iu  the  late  war  in  the  United  States. 
General  Barnard  of  the  United  States  Engineers  de- 
scribes  it   as  follows: 

"  This  (the  revetment)  consisted  of  posts  from  four 
to  six  inches  in  diameter  of  oak,  chesnut,  or  cedar, 
cut  into  lengths  of  5-|-  feet  and  set  with  a  slope  of 
I"  in  close  contact  in  a  trench,  at  the  foot  of  the 
breast  height,  two  feet  in  depth.  These  were  sawed 
off  sixteen  inches  below  the  crest  and  shaped  to  re- 
ceive a  horizontal  capping  piece  of  six-inch  timber, 
hewed  or  sawed,  to  a  half-round,  as  shown  in  the 
sketch." 

The  lower  ends  of  the  posts  rested  upon  a  two- 
inch  plank,  placed  in  the  bottom  of  the  trench.  The 
capping  piece  was  ^  anchored "  in  place,  by  ties 
notched  into  logs  buried  in  the  parapet.  The  slope 
of  f  is  steeper  than  that  assumed  for  the  ordinary 
profile. 

82.  Flank  Revetments. — Plank  is  an  excellent 
material  for  revetments  where  durabihty  and  great 
strength  are  not  required.  The  ease  of  working  and 
convenience  of  handling  are  its  great  advantages. 
When  it  can  be  easily  obtained  and  can  be  spared 
for  the  purpose,  it  will  always  be  used  in  works  of 
hurried  construction. 

Eevetments  may  be  made  with  it  by  driving  posts 
or  pieces  of  scantling  into  the  earth,  three  or  four 
feet  apart,  giving  to  them  the  same  inclination  as  the 


^X)  FIELD    FORTrFrCATWXS. 

interior  slope.  Boards,  in  a  horizontal  position,  fco  re- 
tain the  earth,  are  then  nailed  to  these  scantlings 
or   posts. 

Or,  the  scantlings  may  be  capped,  and  the  boards 
having  been  cut  into  suitable  lengths,  placed  in  an 
upright  position,  similar  to  the  posts  in  the  timber 
revetment,  shown  in  Fig.  26.  The  moisture  of  the 
earth  soon  produces  rot  in  the  boards  and  renders 
the  revetment  a  very  perishable  one. 

83.  Casks,  barrels,  etc.— Casks,  barrels,  and 
materials  of  this  description,  are  frequently  found  in 
numbers  within  the  neighborhood  of  the  work,  and 
can  be  usefully  employed  in  making  temporary  revet- 
ments. The  construction  of  revetments  of  this  kind 
will  be  similar  to  that  in  which  ^^abions  are  used. 

84.  Sand-bags. — Sand-bags  are  sacks  made  of 
strong  canvas,  and  then  filled  partially  with  sand  or 
earth.  They  are  used  quite  frequently,  when  the  other 
materials  for  revetments  can  not  be  easily  procured  ;  or 
where,  from  peculiar  circumstances,  they  can  be  usefully 
employed  to  give  speedy  protection  against  an  enemy's 
fire.  The  sacks  are  usually  made  about  two  feet  and 
three  inches  long,  and  one  foot  and  two  inches  wide, 
when  empty.  They  are  about  three-fourths  filled  with 
earth,  and  are  then  tied  at  the  top. 

The  bags  are  not  entirely  filled  with  earth,  so  that 
they  may  be  flattened  when  laid  in  the  revetment. 
They  are  usually  laid  as  *^  headers  and  stretchers,"  that 


REVETMENTS. 


91 


is,  the  ends  and  sides  of  the  bags  appear  alternately  in 
each  course.  (Fig.  27.)  The  bags  break  joints  in  each 
course.     Sometimes  the  bas-s  are  all  laid  as  headers. 


Ffg.  27. 


It  will  require  eighteen  sand-bags  of  the  size  just 
given,  laid  as  headers  and  stretchers,  to  make  one 
square  yard  of  revetment. 

The  sand-bag  revetment  possesses  peculiar  advan- 
tages, where  speedy  shelter  is  required,  or  where  the 
earth  has  to  be  carried  some  distance  under  fire.  Its 
great  defect  is  the  perishable  nature  of  the  revetment, 
due  to  the  speedy  rotting  of  the  bags. 

Fig.  28. 


Sand-bags  are  very  useful  to  place  on  the  parapet 
of  a  work  to  form  improvised  loop-holes  for  the  de- 
fence. (Fig.  28.) 


92  FIEI^D    FORTIFICATIONS. 

85.  Sod  revetments. — Grass  sods  form  the  best 
revetments  for  the  interior  slopes  and  for  the  cheeks  of 
embrasures. 

Sod  revetments  are  durable  and  do  not  splinter 
when  struck  by  the  enemy's  projectiles.  They 
require  considerable  time  in  which  to  construct 
them. 

Sods  for  revetments  should  be  cut  from  fine,  close 
turf  with  thickly  matted  roots,  the  grass  having  been 
mowed  previous  to  the  cutting.  They  are  cut  in  tke 
form  of  blocks,  16  inches  long,  8  inches  wide,  and  4 
inches  thick. 

The  construction  of  a  sod  revetment  should  be  com- 
menced, when  practicable,  as  soon  as  the  parapet  is 
raised  to  the  level  of  the  tread  of  the  banquette.  The 
first  course  is  then  laid  with  the  grass  side  downwards, 
alternately  as  headers  and  stretchers  ;  or,  two  stretchers 
to  one  header.  The  upper  surface  of  this  layer  sliould 
be  perpendicular  to  the  plane  of  the  interior  slope, 
and  this  position  is  given  to  the  sods  by  sloping  the 
bed  on  which  they  rest. 

The  second  course  is  then  laid  in  a  similar  manner 
on  the  first,  and  breaking  joints  with  it.  Sometimes  a 
few  wooden  pegs  are  driven  through  the  upper  sods 
into  the  lower  ones,  to  fasten  them  together ;  but  this 
is  not  necessary. 

The  other  courses  are  laid  in  a  similar  manner  to 
that  described  for  the  first  and  second,  until   the  top 


REVETMENTS,  9S 

course  is  reached  ;  which  should  be  laid  with  the  grass 
side  upwards. 

Each  course  is  settled  firmly  in  place  by  tapping 
the  sods  as  they  are  laid^  with  the  flat  side  of  a  spade, 
and  packing  the  earth  of  the  parapet  closely  behind 
each  layer. 

It  is  recommended  to  have  the  sods  laid  protruding 
slightly  beyond  the  face  of  the  interior  slope,  so  that 
eacli  course,  after  it  has  been  laid,  may  be  nicely 
trimmed. 

In  the  sod  revetments  used  in  the  Washington  de- 
fences, the  sods  were  eighteen  inches  long,  twelve  inches 
wide,  and  four  inches  thick.  They  were  laid  to  form 
a  sod-"wall,  twelve  inches  thick,  and  with  a  slope  of 
f.  The  earth  of  the  parapet  was  thoroughly  rammed 
behind  the  revetment,  and  was  carried  up  simultane- 
ously with  the  laying  of  the  sods.  The  courses  were 
connected  by  small  wooden  pegs,  three-fourths  of  an 
inch  in  diameter  and  nine  inches  long,  driven  through 
each  alternate  course  into  the  layers  beneath. 

86.  Pisa  Revetment. — A  pisa  revetment  is  a 
wall  of  clay  built  against  a  slope  to  protect  it. 

Its  construction  is  as  follows  :  Common  earth, 
mixed  with  clay  and  moistened  with  water,  is  kneaded 
until  the  particles  will  adhere  when  pressed  or  squeezed 
together.  Sometimes  chopped  straw  is  mixed  in  the 
mass.  A  row  of  pickets,  with  the  proper  inclination 
given  to  them,  is  driven  along  the  foot  of  the  interior 


94  FIELD   FORTIFICATIONS, 

slope,  tlie  tops  extending  a  short  distance  above  the 
height  marked  for  the  interior  crest.  A  shallow 
trench  about  twelve  inches  wi(Je  is  dug  in  the  para- 
pet, behind  the  line  of  pickets,  and  a  board  laid  hori- 
zontally on  edge  on  the  side  next  to  and  supported 
by  the  pickets.  The  tempered  clay  is  then  placed  in 
the  trench  and  rammed.  Successive  layers  are  placed 
in  until  the  clay  reaches  the  top  of  the  board,  the 
earth  of  the  parapet  being  carried  up  simultaneously 
with  the  revetment.  A  second  board  is  then  placed 
upon  the  first,  and  the  clay  rammed  in,  rising  si- 
multaneously with  the  parapet  as  in  the  first  course  ; 
and  this  process  is  continued  until  the  top  layer  is 
on  the  same  level  with  the  interior  crest.  When  the 
clay  has  dried,  the  boards  and  pickets  are  re- 
moved. 

87.  Other  revetments.  —  Sun  -  dried  bricks, 
adobes,  and  stones,  have  been  used  for  revetments. 
They  are  built  into  walls  in  a  method  similar  to  that 
described   for   sods. 

Any  material  which  can  be  used  to  protect  the 
earthern  slope  will  be  suitable.  Time,  durability, 
and  fitness  are  the  things  to  govern  in  the  selection 
of  materials  for  revetments. 

For  batteries  or  parapets  exposed  to  artillery  fire, 
the  fascines  are  preferable  for  revetments.  Gabions 
are  to  be  preferred  for  embrasures  and  traverses ; 
sand  bags  for  powder  magazines  and  traverses.     Some- 


RE  VET3IENTS,  95 

times   all   three   of    them    are    used    simultaneously  in 
the  same  field  work. 

Gabions  require  less  wood  than  fascines,  and  are 
more  easily  made.  They  do  not  have  to  be  tied  or 
fastened  in  place,  like  fascines.  Sand-bag  revetments 
are  more  quickly  made,  but  the  canvas  rots  quickly. 
Sods  are  the  best  material,  but  revetments  made 
from  them  require  a  great  deal  of.  time  and  labor  to 
construct. 


CHAPTER    X. 

'    .  D  EFILA  DE. 

88.  Defilade. — The  first  principle,  enunciated  in 
Art.  7,  imposes  th^  condition  that  the  defenders  of  a 
field  work  should  be  screened  from  the  enemy's  view. 

If  the  work  is  built  upon  a  level  site  which  com- 
mands all  the  ground  around  it,  this  condition  is  ful- 
filled, when  the  space  occupied  by  the  men  is  enclosed 
by  a  parapet  eight  feet  high. 

If  the  work  is  built  upon  an  irregular  site,  or  if 
there  are  heights  within  cannon  range  wliich  com- 
mand it,  a  parapet  of  uniform  height  and  only  eight 
feet  high  will  not  screen  the  men  in  the  interior  from 
the  enemy's  view. 

The  arranging  of  a  work,  under  these  circum- 
stances, so  that  the  men  standing  on  the  terreplein 
behind  the  parapet  shall  be  screened  from  the 
enemy's  view,  and  be  protected  from  his  fire,  is  called 
defilading  the  work. 

There  are  three  ways  which  may  be  used  to  defil- 
ade a  work. 

1.  By  raising  the  parapet. 

2.  By  lowering  the  terreplein. 

3.  By  using  traverses. 


DEFILADE. 


97 


The  labor  of  defilading  may  be  reduced,  and  in 
many  eases  avoided,  by  giving  proper  directions  to 
the  lines  of  the  work. 

89.  Plane  of  defilade. — To  illustrate  this  sub- 
ject, take  a  field  work  built  upon  a  site  which  is 
practically  level,  but  within  cannon  range  of  a  hill 
which  commands  it.     (Fig.  29.) 


Fig.  29. 


It  is  plain  that  if  the  parapet  from  C  ^o  D  is  not 
high  enough,  an  enemy  occupying  a  position  at  M  can 
see  the  defenders  when  standing  on  the  terreplein  be- 
hind the  parapets  of  the  flanks,  A  C  ^^^  B  D. 

It  is  also  plain  that  if  the  parapet  be  raised  high 
enough  to  conceal  the  men  on  the  terreplein  at  A 
and  at  B?  an  enemy  at  |V|  can  not  see  the  defenders 
on  the  terreplein  in  any  portion  of  the  work. 


()8  FIELD   FORTIFICATIONS. 

Safety  for  a  man  at  A  or  B  requires  tliat  the  line 
of  fire  coming  from  M  should  pass  at  least  six  feet 
and  six  inches  above  the  ground  on  which  he  stands 
(Art.  20).  In  other  words,  he  must  be  sheltered  from 
all  fire  of  the  enemy  coming  from  M, 

Let  H  P  represent  a  line  which  passes  eight  feet 
above  the  ground  along  A  B^  and  five  feet  above  the 
ground  at  M  j  this  will  be  a  line  of  the  plane  of 
fire  from  M,  above  which  the  effects  of  direct  fire 
from  M  may  be  neglected.  Any  mass  interposed  be- 
tween the  line  A  B  ^^^^^  the  height  M?  '*^^^  raised 
until  its  top  touches  or  rises  above  the  line  H  P,  will 
intercept  the  direct  fire  on  A  B,  from  |V|>  and  slielter 
the  men  on  the  terreplein  at  the  points  A  and  B, 

If  then  the  interior  crests  S  C  and  S  D  are  held 
in  a  plane  passing  eight  feet  above  the  ground  at  A  B? 
aud  five  feet  above  the  ground  at  M?  the  parapets  of 
these  faces,  S  C  and  S  D?  will  intercept  this  fire, 
and  the  work  will  be  defiladed. 

This  plane  in  which  the  crests  S  C  and  S  D  are 
held  is  known  as  the  plane  of  defilade,  and  may 
be  defined  to  be  that  plane,  which  contabiiiig  the  in- 
terior crest  of  a  work,  passes  at  least  eight  feet  above 
those  poi7its  to  he  sheltered,  and  at  least  five  feet  above 
the  ground  tvhich  can  be  occupied  by  an  enemy  'within 
cannon  range, 

90.  Area  to  be  defiladed.— The  amount  of 
space  in  rear  of  a  parapet  which  is  required  to  be  de- 


DEFILADE.  09 

filaded;  depends  upon  circumstances.  In  some  cases, 
the  entire  space  enclosed,  and  in  others  only  a  part,  is 
to  be  protected  from  this  fire  from  a  commanding 
height.  Thus,  it  is  usual  to  require  that  the  whole 
interior  space  of  an  enclosed  work  should  be  defiladed  ; 
that  the  interior  as  far  as  the  gorge  should  be  defil- 
aded for  a  half-enclosed  work ;  and  that  so  much  of 
the  interior,  or  so  much  of  the  terreplein  behind  the 
parapet,  as  may  be  necessary  for  the  free  movements 
of  the  defence,  should  be  defiladed  in  open  works  or 
lines. 

91.  Method  of  determining  the  plane  of 
defilade. — It  is  not  convenient  in  practice  to  place 
the  eye  at  a  distance  of  eight  feet  from  the  ground, 
nor  is  it  an  easy  thing  to  judge,  from  a  distance,  what 
should  be  the  position  of  a  point  like  P,  which  shall 
be  five  feet  above  the  ground.  The  method  used  is 
to  place  the  eye  at  a  convenient  distance  from  the 
ground,  observe  the  highest  point  of  the  top  of  the 
hill,  and  determine  the  position  of  a  visual  plane  tan- 
gent to  the  hill.  Knowing  the  position  of  this  visual 
plane,  a  second  plane  is  passed  parallel  to  it  and  five 
feet  above  it.  The  tangent  visual  plane  is  known  as 
the  rampant  plane,  and  the  plane  parallel  to  it  is 
the  plane  of  defilade. 

The  position  of  the  rampant  plane  and  the  plane 
of  defilade  may  be  fixed  as  follows. 

To  illustrate  the  method,  a  redan  is  supposed  to  be 


J  00 


FIELD  FORTIFICATIONS. 


the  field  work  which  is  to  be  built,  upon  a  position 
commanded  by  a  neighboring  height,  and  that  the 
salient  and  extremities  of  tlie  faces  are  marked  by 
upright  poles  planted  in  the  ground.     (Fig.  30.)     The 


Fig.  30, 


ii^>^fF^  7!ii^:=^^     —         "  — ^  ..     -  /Ifeir 


trace  marked,  the  next  step  is  to  profile  the  work,  and 
this  requires  the  height  of  the  interior  crest  to  be  de- 
termined. 

Two  stakes,  at  a  convenient  distance  apart,  are 
erected  upon  the  gorge  line  ;  if  not  too  far  apart,  the 
poles  already  erected  to  mark  the  extremities  of  the 
faces  may  be  used.  A  line,  three  feet  from  the 
ground,  is  marked  by  a  strip  of  wood  having  a 
straight  edge,  or  by  a  cord  tightly  stretched,  and 
fastened   to  these   uprights. 

An  observer  is  placed  in  rear  of  this  line  ;  he  sights 
along  it  and  tangent  to  the  hill,  h,  and  determines 
where  the  visual  plane  containing  this  line  cms  the 
pole  placed  at  the  salient.     This  point  is  marked,  and 


DEFILADE.  101 

with  the  line  joining  the  two  uprights  on  the  gorge 
line,  fixes  the  position  of  a  plane  tangent  to  the  hill 
and  three  feet  above  the  ground  at  the  gorge. 

If  on  the  three  posts.  1,  2,  3,  points  be  marked, 
five  feet  above  the  points  of  intersection  of  the  posts  by 
the  rampant  plane,  these  will  be  points  of  a  plane 
which  will  pass  eight  feet  above  the  ground  at  the 
gorge  and  five  above  the  ground  at  h.  If  the  faces 
of  the  redan  are  held  in  this  plane,  the  whole  in- 
terior of  the  redan  will  be  defiladed  from  this  hill, 
and  the  last  plane  determined  will  be  the  plane  of 
defilade. 

The  extremities  of  the  faces  at  the  gorge  have 
parapets  of  the  ordinary  height,  viz.,  eight  feet ;  the 
parapets  from  these  points,  increase  in  height  until  the 
salient  is  reached,  where  the  height  is  the  greatest. 
The  height  of  the  interior  crest  can  then  be  deter- 
mined, at  the  points  where  the  profiles  are  to  be 
placed. 

In  the  previous  chapter,  the  height  of  the  parapet 
is  supposed  to  be  uniform  throughout.  The  site 
being  level,  there  is  no  reason  why  any  one  part  of 
the  interior  crest  should  be  higher  than  another.  It  is 
nevertheless  the  practice,  even  in  this  case,  to  give  ad- 
ditional height  to  the  parapet  at  a  salient,  not  for  the 
purposes  of  defilading  the  interior,  as  just  explained, 
but  to  lessen  the  effect  of  any  enfilading  fire  which  an 
enemy  might  obtain  upon  the  faces,  and  to  allow  for 


102  FIELD  FORTIFICATIONS. 

the   descent  of    the   trajectory  of  a  projectile    which 
might  graze  the  interior  crest  at  the  salient. 

92.  A  slight  deviation  from  the  method  just  des- 
cribed is  made  when  the  work  to  be  defiladed  is  a  lu- 
nette, instead  of  a  redan  (Fig.  29). 

Two  uprights,  about  twelve  feet  apart,  are  planted 
upon,  and  near  the  centre  of,  the  gorge  line.  A  third 
upright  is  placed  in  front  of  the  gorge  and  ten  or  twelve 
feet  from  it,  upon  the  line  joining  the  centre  of  the 
gorge  line  with  the  salient. 

The  points  are  then  marked  where  the  rampant 
plane,  three  feet  above  the  ground,  cuts  these  three 
uprights  aud  the  uprights  planted  at  the  salient,  S^ 
and  at  the  shoulders,  C  ^.nd  D-  ^  distance  of  five 
feet  is  marked  above  the  points  just  determined,  and 
this  will  fix  the  position  of  the  plane  of  defilade  for 
the  lunette. 

93.  Front  and  reverse  defilade. — The  sup- 
position has  been  made  that  there  is  only  one  com- 
manding height  within  cannon  range  of  the  field  work. 
Suppose  that  there  are  two  or  more  heights,  from  each 
of  which  an  enemy  could  see  the  interior  of  the  work, 
if  an  ordinary  uniform  height  of  parapet  is  used. 

Take  the  case  of  a  redan.  There  are  two  distinct 
conditions  which  may  arise.  One  of  them  is  where 
all  the  heights  will  lie  within  the  angle  of  the  faces 
prolonged  ;  the  other  is  when  one  or  more  of  these 
heights  will  lie  without  this  angle.     Thus,  the  redan. 


DEFILADE, 


103 


A  S  B,  (Fig.  31)  has  the  heights  Z  and  Z' ,  lying 
within  the  angle  of  the  faces  prolonged  ;  and  the 
heights,  X  and  Y^  Iji^^^g  without  this  angle. 

Fig.  31. 


The  heights  Z  and  2J  can  only  bring  front  fires, 
direct  or  slant,  upon  the  faces  of  the  redan.  The 
height  X  can  bring  a  direct  fire  upon  the  face  A  S?  and 
a  reverse  fire  upon  the  face  B  S-  A  similar  condition 
exists  for  the  height  Y. 

The  arrangements  made  to  screen  the  terrepleins 
from  the  front  fire  are  all  made  like  those  just  de- 
scribed, and  give  rise  to  the  problem  known  as  front 
or  direct  defilade.  Those  made  to  screen  the  ter- 
replein  and  the  men  on  the  banquettes  from  reverse 
fires  give  rise  to  the  problem  of  reverse  defilade. 

The  method  used  to  defilade  a  work  from  two  or 
more  heights,  when  these  heights  can  only  bring  front 


KM  FIKL I)    FOR TIFICA TJOyS. 

tires,  is  the  siime  in  principle  iis  that  used  for  a  single 
height.  It  is  only  necessary  in  a  case  of  this  kind  to 
defilade  the  work  from  that  height  which  gives  the 
highest  fire. 

When  some  of  the  heights  expose  the  work  to  a 
reverse  fire,  it  is  usual  to  defilade  the  faces  separately 
from  the  front  fire,  and  then  make  the  necessary  ar- 
rangements to  protect  the  interior  against  reverse  fire. 

94.  Method  used  to  defilade  a  -work  ex- 
posed to  reverse  fire. — The  first  step,  as  has  just 
been  stated,  is  to  defilade  the  work  from  the  front  fire. 
It  is  evident,  even  when  this  is  done,  that  men  upon 
the  banquette  are  exposed  to  reverse  fire. 

Thus,  suppose  a  redan  like  that  in  Fig.  31,  to  have 
had  its  faces  defiladed  from  front  fire.  It  is  plain  that 
men,  standing  on  the  banquette  at  B?  would  be  above 
the  plane  of  defilade  containing  the  face  A  S-  ^^^^ 
would  be  seen  by  an  enemy  at  X-  Suppose  the  interior 
crest  of  the  face,  A  S?  to  be  raised  high  enough  to 
shelter  the  men  on  the  banquette  of  the  opposite  face. 


B  S-  The  effect  would  be  to  shelter  the  men  there, 
but  to  expose  the  men  on  the  banquette  of  the  face 
A  S.      Thus,  if  the  crest  at  C>  (Fig.  32),  is  raised  to 


DEFILADE.  105 

shelter  the  men  on  the  banquette  at  D,  it  exposes  the 
crest  at  F  to  a  fire  coming  from  £•  The  defect  of  re- 
verse fire  is  not  removed,  but  only  transferred  to  an- 
other place  by  raising  the  parapet.  This  method  can 
not  be  used. 

The  method  that  is  used  is  to  interpose  an  auxiliary 
mass  which  shall  intercept  the  dangerous  reverse  fire. 
A  mass  of  earth,  placed  across  a  line  of  fire  to  in- 
tercept the  missiles  moving  along  that  line,  is  termed 
a  traverse.  Thus,  if  a  traverse  of  earth  is  placed 
between  the  banquettes  and  made  thick  enough  to 
protect  the  men,  and  high  enough  to  intercept  the 
enemy's  missiles,  the  men  can  stand  on  the  banquettes 
without  fear  of  the  reverse  fire. 

The  thickness  of  a  traverse,  like  that  of  the  para- 
pet, depends  upon  the  penetration  of  the  enemy's  pro- 
jectiles. 

The  height  of  the  traverse  depends  upon  the  height 
of  that  plane  of  reverse  fire,  above  which  the  fire 
may  be  neglected.  This  plane  which  determines  the 
height  of  the  traverse  is  known  as  the  plane  of  re- 
verse defilade.  It  may  be  defined  to  be,  that 
plane  ivliich  passes  at  least  two  feet  above  the  interior 
crest  exposed  to  reverse  firey  and  at  least  five  feet 
above  the  ground  from  ^vhich  this  fire  can  come. 

When  both  faces  of  the  work  are  exposed  to  re- 
verse fire,  there  will  be  two  planes  of  reverse  defilade. 
In  this  case,  the  least  height  of  the  traverse  will  be 


106  FIELD   FORTIFICATIONS, 

determined  by  the  intersection  of  these  planes  of  de- 
filade, and  the  line  of  intersection  will  form  the  mid- 
dle line  of  the  top  of  the  traverse.  If  it  be  more 
convenient  to  place  the  traverse  along  some  other 
line,  the  capital  for  instance,  the  height  of  the  tra- 
verse will  be  determined  by  the  higher  of  the  two 
planes. 

A  traverse  placed  along  the  capital  frequently 
crowds  the  salient  too  much  ;  in  which  case,  its  direc- 
tion is  changed  when  near  the  salient,  and  it  is  joined 
to  the  face  most  exposed.  (Fig.  31.) 

95.  Method  of  determining  the  plane  of 
reverse  defilade. — Since  a  traverse  is  to  be  used, 
it  will  be  supposed  that  its  place  is  along  the  capital. 
This  traverse  will  divide  the  interior  space  into  two 
equal  parts.  It  will  only  be  necessary  to  defilade  each 
half  from  the  front  fire  ;  which  may  be  done  as  fol- 
lows : 

Uprights  are  placed  along  the  capital  to  mark  the 
middle  of  the  traverse.  A  line,  three  feet  from  the 
ground,  is  marked  upon  these  uprights  by  stretching 
a  cord,  or  by  nailing  strips  of  wood  to  the  poles. 
The  rampant  planes  passing  through  this  line,  and 
tangent  to  the  hills  on  each  side  which  furnish  the 
highest  front  fire,  are  then  determined,  and  their  inter- 
sections with  the  uprights  placed  along  the  sub-crests 
of  the  faces,  are  marked.  On  these  verticals  the 
planes  of    front  defilade  are    then  marked,  and  these 


DEFILADE,  107 

points,  thus  obtained,  determine  the  height  of  the  in- 
terior crests  of  the  faces.  The  profiles  are  then  placed 
along  the  sub-crest  at  the  proper  points. 

The  next  step  is  to  determine  the  position  of  the 
planes  of  reverse  defilade. 

To  illustrate  the  method,  it  will  be  shown  how 
the  plane  of  reverse  defilade  is  found  for  the  face, 
S  B'  o^  the  redan  in  Fig.  31,  which  is  exposed  to  a 
reverse  fire  from  the  high  ground  at  X, 

It  is  supposed  that  the  faces,  S  A  ^"^  S  B?  have 
been  defiladed  from  front  fire  by  the  method  just  de- 
scribed ;  that  the  profiles  of  the  parapet  have  been 
erected  ;  and  that  the  vertical  poles,  marking  the  po- 
sition of  the  middle  line  of  the  traverse,  are  in  place. 

Two,  or  more  of  the  profiles  along  the  face  S  B 
are  taken,  and  are  joined  by  a  straight  line  which 
is  just  three  feet  below  the  interior  crest  of  this 
face,  measured  on  these  profiles.  The  position  of 
this  line  is  fixed  usually  by  marking,  on  the  ver- 
tical on  the  sub-crest  of  each  profile,  a  distance  of 
eighteen  inches  above  the  banquette,  and  by  joining 
the  points  thus  determined  by  a  strip  of  wood  or  a 
tightly  stretched  cord  fastened  to  the  profiles. 

An  observer  is  placed  behind  this  line  and  deter- 
mines the  position  of  a  visual  plane  which  contains  the 
line,  and  is  tangent  to  the  hill,  Xi  The  points  of  in- 
tersection of  this  visual  plane  with  the  poles  placed  to 
indicate  the    position    of    the    traverse,    are   marked. 


108  FIELD  FORTIFICATIONS. 

These  points  marked  on  the  poles,  with  the  line 
three  feet  below  the  crest,  fix  the  position  of  the 
rampant  plane  for  the  reverse  defilade.  The  distance 
of  fiYQ  feet  above  this  plane,  is  marked  upon  these 
poles,  and  the  points  marked  thus  will  be  points  of 
the  plane  of  reverse  defilade,  and  will  determine  the 
height  of  a  traverse  required  to  protect  the  face  B  S 
from  the  reverse  fire  from  X- 

A  similar  process  determines  the  plane  of  reverse 
defilade  for  the  face  A  S- 

The  position  of  the  higher  plane  will  determine 
the  height  which  is  to  be  given  to  the  traverse.  The 
form  of  a  traverse  and  its  construction  will  be  men- 
tioned hereafter. 

96.  Defilade  by  traverses. — The  problem  of 
reverse  defilade  is  almost  always  solved  by  the  use  of 
traverses.  That  of  front  defilade,  by  either  raising 
the  parapet  or  lowering  the  terreplein.  The  latter 
plan  is  the  method  pursued  in  permanent  fortifica- 
tions ;  it  is  sometimes  used  in  ordinary  field  works, 
but  rarely,  because  the  terreplein  and  surface  of  the 
ground  are  generally  one  and  the  same. 

It  is  not  always  practicable  to  solve  problems  of 
front  defilade  in  field  works  by  raising  the  parapet, 
because  the  height  required  for  the  parapet  to  reach 
the  plane  of  defilade  m.ay  be  too  great,  and  exceed 
the  limit  laid  down.     In  these  cases,  traverses  are  used. 

As  an  example,    take  a  lunette  couunanded  by  a 


DEFILADE. 


109 


hill,  as  X  (Fig-  33)  and  suppose  that,  with  a  com- 
mand of  twelve  feet  at  the  salient,  the  interior  crest 
protects  only  half  of  the  interior  of  the  work. 


Fig.  33 


D B^ 


C        A 


The  remaining  half  can  only  be  protected  by  means 
of  a  traverse,  P,  placed  along  the  line  dividing  the 
part  which  is  defiladed  from  that  which  is  not.  Two 
short  traverses  would  be  i3laced  near  the  shoulder 
angles,  overlapping  the  ends  of  the  principal  traverse, 
as  shown  in  the  figure,  with  room  between  the  tra- 
verses to  allow  of  a  passage-way. 

The  short  traverses  at  C  ^^i^  D  would  be  used, 
even  if  p  were  not,  to  protect  the  men  on  the  ban- 
quettes of  the  flanks  from  slant  reverse  fires  coming 
from  H  and    K- 

If  this  traverse  P  is  placed  in  the  work  to  shelter  the 
men  from  a  fire  in  the  opposite  direction,  which  would 
be  a  reverse  fire  upon  the  faces,  it  is  termed  a  parados, 
a  name  employed  to  designate  the  traverse  when  it  is 
used  to  intercept  a  reverse  fire  of  this  kind. 

The  great  objections  to  the  use  of  traverses  are  the 
space  they  take,  and  the  labor  they  require  for  their 
construction.      When   built  they  are  often   utilized  in 


110 


FIELD  FORTIFICATIONS. 


other  ways,  besides  the  primary  use  as  an  intercept- 
ing mass. 

97.  Defilade  of  lineis. — The  same  methods  may 
be  used  to  defihide  an  open  work,  a  part  of  a  line, 
or  a  line,  as  are  used  to  defilade  a  half-closed  or  a 
closed  work. 

The  longest  sides,  or  the  faces,  of  an  open  work 
or  a  line  should  be  traced,  where  practicable,  perpen- 
dicular to  the  direction  of  the  enemy's  fire  ;  and 
should  be  located,  if  possible,  so  that  the  parapet 
shall  occupy  a  ridge,  or  be  so  situated  that  the 
ground  in  rear  of  the  parapet  shall  slope  away  from  it. 

A  line  traced  and  placed  in  this  way  will,  for  the 
same  height  of  parapet,  defilade  a  larger  extent  of 
terrepjein  than  it  would  if  its  direction  were  inclined 
to  that  of  the  fire,  or  the  parapet  were  placed  upon 
ground  which  was  level,  or  which  sloped  towards  the 
enemy. 

When  the  commanding  ground  is  a  ridge  or    suc- 


Fig.  34. 


»'# 


cessions  of  hills  on  the  same  general  level,  the  direc- 
tion of  the  line  should  be  parallel  to  the  general  direc- 
tion of  the  ridge.    (Fig.   34). 


DEFILADE.  Ill 

The  simple  right  line  with  a  uniform  relief  will,  in 
this  case,  defilade  the  terreplein  jnore  efficiently  than 
if  the  line  were  broken,  since  the  general  direction  of 
the  line  is  perpendicular  to  the  general  fire  coming 
from  the  heights. 

If,  however,  a  broken  line  is  to  be  used,  a  contin- 
ued redan  line  for  example,  it  is  recommended  to 
make  the  salients  of  the  large  redans  as  obtuse  as  pos- 
sible. By  so  doing,  the  perpendicular  distance  be- 
tween the  salients  and  re-entrants  is  shortened,  and 
the  long  faces  are  made  more  nearly  perpendicular 
to  the  enemy's  close  fire. 

If  the  ridge  is  not  too  high,  and  the  distance  from 
the  salient  to  the  re-entering  is  not  too  great,  it  will 
be  practicable  to  hold  the  interior  crest  of  the  line  in 
a  plane  of  defilade,  and  not  have  the  height  of  the 
parapet  too  great  at  the  salients.  Moreover,  the  ob- 
tuseness  of  the  salients  will  cause  the  prolongations 
of  the  faces  to  intersect  the  high  ground  at  distances 
so  great,  that  the  enfilade  fire  from  these  points  mav 
be  disregarded.  If  the  heights  are  not  on  the  same 
general  level  but  slope  downwards  to  the  plane  of 
site,  a  better  position  for  the  line  is  one  which  is 
obhque  to  the  crest  of  the  ridge.  A  direction 
should  be  given  to  the  line,  so  that  its  front,  pro- 
longed, would  pass  through  the  point  in  which  the 
meridian  line,  or  vertical  contour,  of  the  ridge  pierces 
the    plane    of    site.      Thus,   a  ridge   of  high  ground. 


112 


FIELD   FORTIFICATIONS, 


sloping  downwards  from  X  to  Y  (Fig.  35),  commands 
the  ground,  A  B,  on  which  a  line  of  fortification  is 
to  be  built. 


Fig.  36 


The  vertical  contour  line  of  the  ridge  is  the  intersec- 
tion of  a  vertical  meridian  plane  with  the  ridge, 
which  line  is  projected  upon  the  plane  of  site  in  the 
dotted  line  X  Y,  and  pierces  this  plane,  in  this  case, 
at  B.  The  front  of  the  line  should  have  a  direction 
like  A  B. 

In  this  position  a  plane  can  be  passed  in  which 
the  salients,  with  a  uniform  command,  may  be  held, 
and  the  terrepleins  be  defiladed  from  the  high  ground 
in  front. 

A  straight  line  of  parapet  would,  in  this  case, 
afford   the   best   cover   for    the   terreplein   behind    the 


DEFILADE.  113 

parapet,  as  it  would  in  the  case  where  the  line  is 
taken  parallel  to  the  commanding  ground. 

But,  if  a  broken  line  be  used,  care  should  be  taken, 
as  in  the  last  case,  to  make  the  salients  obtuse 
angles.  If  the  line  be  a  bastioned  line,  it  is  plain 
that  the  flanks  are  liable  to  be  exposed  to  both  reverse 
and  enfilading  fires. 

The  nearer  the  angle  A  B  X  is  to  a  right  angle,  the 
better  will  be  the  position  of  the  line  A  B  tc>  allow  of 
its  terreplein  being  defiladed  from  the  high  ground  in 
front. 


CHAPTER    XL 

THE   INTERIOR   ARRANGEMENTS   OF    A   FIELD    WORK. 

98.  Classes. — The  earth  work  for  the  parapet 
being  completed,  and  the  revetments  of  the  interior  slope 
constructed,  attention  is  then  paid  to  the  interior  of  the 
work.  Certain  arrangements  have  to  be  made  in  the 
interior,  to  add  to  the  efficiency  of  the  defence,  and 
to  provide  for  the  comfort  of  the  troops  who  have  to 
occupy  the  work.  These  interior  arrangements  are 
divided  into  classes,  according  to  the  object  to  be 
attained  by   tliem. 

The  divisions  may  be  classified  as  follows  : 

1.  The  arrangements  of,  and  along  a  parapet,  in- 
tended to  add  to  the  efficiency  of  the  defence  ; 

2.  The  arrangements  within  the  area  enclosed  by 
a  parapet,  to  shelter  the  men  and  materiel  from  the 
fire  of  the  enemy  : 

3.  The  arangements  made  to  allow  egress  and 
ingress  of  the  troops  ;  inclnding  those  made  to  guard 
the  entrances  against  surprise  ;  and 

4.  The  arrangements  which  may  be  made  to  pro- 
vide for  the  comfort  and  welfare  of  the  garrison  when 
occupying  the  interior  of  the  work  for  some  time. 


INTERIOR   ARRANGEMENTS   OF  A   FIELD    WORK.    115 

I.    Arrangement  of  the  Parapet. 

99.  Defence. — The  work  may  be  defended  by 
musketry  alone,  or  it  may  be  defended  by  artillery 
combined  with  musketry. 

The  arrangements  of  the  parapet  for  musketry  are 
completed  when  the  banquette  and  the  revetment  of 
the  interior  slope  are  finished. 

The  work,  in  this  condition,  does  not  admit  of  the 
use  of  artillery.  Some  additional  arrangements  must 
be  provided,  if  artillery  is  to  be  employed.  The  fire 
of  artillery  is  either  over  the  parapet  Or  through  it. 
In  the  former  case,  the  fire  is  said  to  be  '^  en  barbette;  " 
in  the  latter,  it  is  called  *^  embrasure  fir e.^'^  In  both  of 
these  fires,  arrangements  must  be  made  in  or  along 
the  parapet  for  the  service  of  the  guns. 

100.  Barbette  fire. — Barbette  fire  can  only  be 
obtained  by  some  arrangement  which  raises 'the  gun 
into  a  position  from  which  it  can  be  fired  over  the 
parapet.  There  are  two  methods  by  which  this  can  be 
done  ;  one,  by  mounting  the  gun  on  a  high  carriage,  or 
on  a  carriage  which  admits  of  the  gun  being  raised  to 
the  necessary  position ;  the  other,  by  building  a  mound 
of  earth  sufficiently  high  behind  the  parapet,  and 
placing  the  gun  on  this  mound.  The  latter  is  the 
method  generally  employed  in  field  works. 

This  mound  of  earth  in  rear  of  the  parapet,  with 
its  upper  surface  arranged  so  that  a  piece  of  artillery 


116  FIELD  FORTIFICATIONS. 

placed  upon  it  can  fire  over  the  parapet,  is  called  a 
barbette. 

The  artillery  used,  in  the  defence  of  field  works, 
may  be  either  siege  or  field  guns  ;  but  most  gener- 
ally the  latter  are  employed. 

The  upper  surface  of  the  platform  on  which  the 
wheels  rest,  or  the  upper  surface  of  the  barbette,  when 
no  platform  is  used,  should  be  at  a  distance  below  the 
interior  crest  just  sufficient  to  allow  the  gun  to  fire 
over  the  interior  crest  and  parallel  to  the  superior  slope. 
A  distance  greater  than  this  would  interfere  with  the 
efficiency  of  the  gun  ;  a  distance  less,  would  unneces- 
sarily expose  the  gun  and  carriage  to  the  enemy's  fire. 

The  axis  of  the  trunnions  of  a  field  gun,  in  the 
United  States  service,  is  about  forty-three  (43)  inches 
above  the  ground  on  which  the  wheels  rest.  The 
diameter  of  the  piece  at  the  muzzle  and  the  inclination 
of  the  superior  slope  being  given,  it  is  easy  to  deter- 
mine what  should  be  the  distance  of  the  upper  sur- 
face of  the  barbette  below  the  interior  crest. 

The  general  rule  used  is  to  take  this  distance  at 
two  feet  and  nine  inches  for  field  guns,  and  four  feet 
for  siege  guns,  when  mounted  upon  the  ordinary  car- 
riages. 

101.  Construction  of  the  trace  of  a  bar- 
bette.— The  trace  of  a  barbette  for  a  single  field  gun 
behind  the  parapet  of  one  of  the  faces  of  a  work,  may 
be  constructed  as  follows  : 


INTER  TOR   ARRANGEMENTS   OF  A    FIELD    WOBK.    11? 

Let  A  B  (Fio-  3^)  be  the  interior  crest  of  the 
face,  and  Q  tlie  point  at  which  the  barbette  is  to  be 
constructed. 

Fig.  36. 


Superior  Slope 


Banquette 


The  upper  surface  of  the  barbette  is  to  be  made 
level,  and  large  enough  to  allow  the  working  of  the 
gun. 

A  field  gun  firing  over  a  straight  parapet  requires 
a  front  of  ten  feet,  at  least,  and  should  have  a  depth 
of  twenty  feet,  to  allow  for  the  recoil  and  proper 
handling  of  the  piece.  Since  the  upper  surface  of 
the  barbette  is  thirty- three  inches  below  the  interior 
crest,  its  intersection  with  the  interior  slope  will  be 
a  straight  line,  a  h,  parallel  to  A  B?  and  eleven  inches 

0"F  THR  \ 


118  FIELD   FORTIFICATIONS. 

from  it  in  projection.  Make  a  h  equal  to  the  re- 
quired length  of  front  (taken  to  be  fifteen  feet  in 
this  case)  and  througli  the  extremities,  draw  the  lines 
a  c  and  b  d  perpendicular  to  a  b,  making  them  each 
equal  to  twenty  feet.  The  area  abed  will  be  the 
u})per  surface  of  the  barbette,  in  plan.  The  upper 
surface  of  the  barbette  is  joined  to  the  site  by  the 
natural  slope  of  the  earth,  which  is  assumed  to  be  4^. 

The  height  of  the  parapet  is  eight  feet,  which  fixes 
the  height  of  the  barbette  at  five  feet  and  three 
inches.  The  intersections  of  the  natural  slopes  of  the 
sides  and  rear  with  the  plane  of  site  are  then  easily 
determined,  as  well  as  the  intersections  with  the  ban- 
quette tread  and  the  banquette  slope.  These  intersec- 
tions determined,  the  construction  of  the  trace  is  com- 
pleted. 

The  gun  is  carried  to  the  top  of  the  barbette  by 
an  inclined  road,  called  a  ramp,  connecting  the 
upper  surface  of  the  barbette  with  the  plane  of  site. 
The  ramp,  f  g  f  g',  has  a  width  of  nine  feet  and  a 
slope  of  ^.  and  is  here  placed  at  the  rear  of  the 
barbette.  The  width,  the  slope,  and  the  position,  are 
all  governed  by  convenience  and  the  circumstances 
of  each  case. 

The  sides  of  the  ramp  are  joined  to  the  site  by 
the  natural  slope  of  the  earth. 

102.  Barbettes,  when  used,  are  almost  always  placed 
in    th.e    salients.      Their    construction    is    practically 


TXTERIOR   ARRANG EMENTS    OF  A    FIELD    WORK,    110 

the  same  as  when  placed  against  the  face  of  a  work. 
It  is  usual,  when  a  barbette  is  made  in  a  salient,  to 
fill  the  salient  angle  for  a  short  space  with  earth,  and 
to  form  a  short  face,  called  a  pan-coup^,  (Fig.  37), 

Fig.  37. 


/ 

/ 

A 

\ 

\ 

=7 

/ 

over  which  the  gun  fires  in  the  direction  of  the  capi- 
tal. The  length  of  this  pan-coupe  is  from  ten  to 
fifteen  feet. 

The  construction  of  the  plan  differs  from  the  one 
described  only  in  the  form  of  the  upper  surface.  In 
this  case,  the  upper  surface  is  pentagonal  in  form,  care 
being  taken  to  make  it  large  enough  to  allow  the  gun 
to  be  fired  over  the  faces  of  the  salient,  as  well  as  along 
the  capital. 


120  FIELD   FOBT/FWATWKS. 

In  this  particular  case,  ifc  is  arranged  for  only  one 
gun.     It  may  be   arranged  for  several. 

103.  Embrasure  fire. — The  opening  made  in  a 
parapet  to  allow  a  piece  of  artillery  to  fire  through 
it,  is  called  an  embrasure. 

The  gun  may  rest  upon  the  natural  surface  of  the 
ground  in  rear  of  the  parapet,  or  it  may  be  placed 
upon  a  mound  of  earth  similar  in  shape  to  a  bar- 
bette, only  not  so  high. 

The  bottom  of  the  embrasure,  in  either  case,  must 
be  placed  so  that  the  gun,  resting  on  its  platform  can 
fire   through  the   embrasure   when  run    ^^  in   battery.'' 

The  bottom  of  an  embrasure  is  called  the  sole.     It 

« 

is  given  an  inclination,  to  allow  the  gun  to  be  fired 
with  its  muzzle  depressed.  This  inclination  is  usually 
taken  to  bQ  the  same  as  that  of  the  superior  slope  of 
the  parapet,  unless  otherwise  stated. 

The  opening,  a  b  Q  W^  (Fig.  38),  in  the  interior 
slope  is  called  the  throat,  and  should  be  made  as 
small  as  practicable.  It  is  usually  made  from  eigh- 
teen to  twenty-four  inches  wide,  and  either  rectangular 
or  trapezoidal  in  form. 

The  embrasure  widens  towards  the  exterior,  the 
amount  of  widening  depending  upon  the  extent  of  field 
of  fire  required.     This  widening  is  called  the  splay. 

The  sides  of  the  embrasure  are  called  the  cheeks  • 
the  line,  M  N?  which  bisects  the  sole  is  called  the 
directrix. 


INTERIOR   ARRANGEMENTS   OF  A    FIELD    WORK.    1;21 

The  portion  of  the  interior  slope  which  is  below 
the  throat  of  the  embrasure  is  termed  the  genouill- 
ere  •  the  mass  of  parapet  between  two  embrasures 
is  termed  a  merlon. 


f                           Superior  Slope        J 

B             \ 

L                                 / 

^--^ 

Banquette            f 

, 

/ 

{ 

..._LJ 
i 

I 
M 


The  embrasures  in  field  works  are  usually  cut  after 
the  parapet  has  been  constructed,  and,  in  important 
works,  the  exterior  openings  are  masked  until  the 
moment  to  use  them  arrives,  to  prevent,  their  position 
being  discovered  by  reconnoitering  parties  of  the 
enemy.  A  detail  of  six  men  should  be  able  to  cut  an 
embrasure  in  the  parapet  of  a  field  work  and  finish 
it  in  eight  hours. 

104.  Trace  of  an  embrasure.— To  make  the 
trace  of  an  embrasure,  draw  the  line  M  N.  (Fig.  38), 
perpendicular  to  the  interior  crest,  at  the  point  where 
the  line  of  fire  of  the  ffun  intersects  it,  and  set  off  a  h 


122  FIELD   FORTIFICATIONS. 

equal  to  the  width  of  the  throat  at  the  top.  If  the 
throat  is  to  be  rectangular,  draw  through  a  and  b 
the  lines  a  G  and  h  H,  perpendicular  to  the  interior 
crest,  and  produce  them  until  they  intersect  the  line, 
G  H.  drawn  parallel  to  the  interior  crest  and  at  a  dis- 
tance from  it  equal  to  one-third  of  the  depth  of  the 
throat.     This  gives  the  plan  of  the  throat. 

To  trace  the  plan  of  the  sole,  ^the  inclination  and 
splay  must  be  known.  Knowing  these,  the  intersec- 
tion of  the  sole  with  the  exterior  slope  can  be  deter- 
mined. This  intersection  may  be  determined  as  fol- 
lows: 

Construct  a  profile  of  the  parapet,  and  find  the 
point  in  which  the  line  G  H  pierces  it.  Through  this 
point  thus  determined  draw  a  line  in  the  plane  of  the 
profile,  making  the  same  angle  with  the  horizontal 
that  the  sole  makes  with  the  horizontal  plane,  and 
find  the  point  in  which  this  line  intersects  the  ex- 
terior slope.  This  point  of  intersection  is  a  point  of 
the  line  E  F,  which  line  is  parallel  to  the  exterior 
crest. 

The  splay  of  the  sole  is  usually  determined,  in  plan, 
by  giving  to  E  p  some  definite  length,  and  then  joining 
its  extremities  with  the  lower  line  of  the  throat.  A 
throat  twenty  inches  wide  will  have  a  horizontal  field 
of  fire  of  twenty-two  degrees,  when  E  F  is  equal  to  one 
half  the  thickness  of  the  parapet ;  a  fire  of  thirty- one 
degrees,  when  the    E  F  is   equal   to   two-thirds   of  the 


INTERIOR   ARRANGEMENTS    OF  A    FIELD    WORK.    123 

thickness ;  a  fire  of  forty-eight  degrees,  when  this 
line  is  equal  to  the  thickness  of  the  parapet. 

Supposing  twenty  degrees  to  be  the  field  of  fire 
required,  E  F  is  made  equal  to  half  the  thickness  of 
the  parapet,  and  the  points  E  and  p  are  then  joined  to 
G  and  H?   which  completes  the  plan  of  the  sole. 

The  cheeks  are  determined  by  setting  off  on  the 
exterior  crest,  on  the  right  and  the  left  of  the  sole, 
points  as  C  and  \),  the  horizontal  distances  of  which 
from  the  lines  E  G  and  p  H?  measured  on  the  line 
C  D^  shall  be  equal  to  one-third  of  their  height  above 
the  sole  ;  and  then  joining  these  points  to  a  and  h,  and 
to  E  and  F>  by  straight  lines.  These  lines  complete 
the  plan  of  the  embrasure. 

The  cheeks  are  warped  surfaces  which  may  be  gen- 
erated by  moving  a  straight  line,  touching  the  sides 
of  the  throat,  and  the  sides  of  the  opening  in  the 
exterior  slope,  so  that  the  intersection  of  the  surfaces 
with  the  sole  and  the  superior  slope  shall  be  straight 
lines. 

The  cheeks  should  be  revetted  for  several  feet  at 
least  from  the  throat,  to  protect  them  from  the  weather 
and  the  blast  of  the  guns.  Gabions  are  usually  em- 
ployed for  this  purpose,  and  are  covered  in  action  with 
raw-hides  when  they  can  be  procured.  Sods  make 
good  revetments  fcTr  the  cheeks,  if  there  is  time  to 
finish  them. 

Consecutive    embrasures    should    not  be    nearer  to 


124  FIELD   FOirriFJCATrONS, 

each  other  than  fifteen  feet  from  centre  to  centre,  to 
prevent  crowding  of  the  guns,  and  to  prevent  the  mer- 
lon,   M,    (Fig.   39)    from   being  too   weak.      A   merlon 
Fig.  39. 


ZL 


3 


which  measures  less  than  six  feet  on  the  exterior  crest 
should  not  be  allowed,  as  it  would  make  the  parapet 
too  weak. 

105.  Direct  and  oblique  embrasures. — A 
direct  embrasure  is  one  in  which  the  directrix  is  per- 
pendicular to  the  interior  crest  at  the  point  of  intersec- 
tion with  the  crest ;  an  oblique  embrasure  is  one  in 
which  the  directrix  makes  an  angle  with  the  interior 
crest.  When  possible,  direct  embrasures  are  the  ones 
which  are  made.  If  oblique  embrasures  are  to  be 
made,  their  method  of  construction  is  practically  the 
same  as  that  given  for  direct  embrasures. 

Oblique  embrasures  do  not  admit  of  the  muzzle 
of  the  gun  being  inserted  so  far  as  the  direct  ones, 
and   they  weaken  the  parapets  more. 

Oblique  embrasures  are  not  used,  as  a  rule,  if  the 
directrix  makes  with  the  normal  to  the  crest  an  angle 
exceeding  ten  degrees.  In  case  the  angle  is  greater, 
the  embrasure  is  provided  for,  in  field  works,  by  modi- 
fying the  interior  crest  by  means  of  the  method 
known  as  ^'indenting." 


INTERIOR   ARRANGEMENTS    OF  A   FIELD    WORK,-   125 

This  method  consists  in  making  the  crest  a  cre- 
maillere  line,  instead  of  a  right  line,  with  the  short 
branches  perpendicular  to  the  direction  of  the  fire,  and 
in  these  short  branches  constructing  direct  embrasures. 
106.  Comparative  advantages  and  defects 
of  the  two  kinds  of  fire. — The  advantages  of 
barbette  fire  in  a  field  work  consist  in  its  wide  field  of 
fire,  its  commanding  position,  and  its  not  weakening 
the  parapet  to  obtain  this  fire.  The  main  defect 
is  the  exposure  of  the  men  and  guns  to  the  enemy's 
fire. 

The  advantages  of  embrasure  fire  over  the  barbette 
are,  that  the  men  serving  the  guns,  and  the  guns 
themselves,  are  boch  protected  to  a  greater  degree  from 
the  enemy's  fire.  The  defects  are,  its  limited  field  of 
fire,  its  weakening  the  parapet  to  obtain  this  fire,  the 
constant  repairing  of  the  cheeks  of  the  embrasures 
when  in  use,  and  the  good  mark  the  embrasures  offer 
to  the  enemy. 

107.  Bonne ttes. — It  is  frequently  desirable  that 
the  height  of  the  parapet,  at  certain  points,  should 
be  increased  for  a  short  distance.  This  increase  is 
generally  obtained  by  making  use  of  the  constructions 
known  as  bonnettes.  A  bonnette  extends  but  a 
short  distance  along  the  parapet,  is  made  of  earth, 
and  is  used  generally  to  give  greater  protection  to  the 
men  standing  on  the  banquette  against  a  slant  or  an 
enfilading  fire  of  the  enemy. 


126  FIELD  FORTIFICATIONS, 

Bonnettes  are  placed  usually  on  the  salients  ;  they 
are  sometimes  placed  on  the  parapet  between  guns 
'^ en  harhette,^^ 

They  may  be  constructed  during  the  progress  of 
the  work,  or  after  the  work  has  been  finished.  In 
the  former  case,  their  construction  is,  to  all  intents 
and  purposes,  similar  to  that  of  the  parapet.  In  the 
latter  case,  they  are  constructed  generally  in  haste, 
and  sand  bags  or  gabions  filled  with  earth  are  used 
to  build  them. 

108,  Loop-holes. — Troops  on  the  banquette, 
when  in  the  act  of  firing  their  pieces,  are  frequently 
exposed  to  the  fire  of  the  enemy's  sharp-shooters. 
Under  these  circumstances,  expedients  must  be  devised 
to  protect  the  men,  without  interfering  with  their 
fire.  The  expedient  which  is  most  generally  used,  is 
that  of  an  improvised  loop-hole.  The  loop-hole  is 
made,  in  this  case,  by  arranging  two  or  more  rows  of 
sand  bags,  placed  upon  the  parapet  and  filled  with 
earth,  so  that  the  top  row  will  be  higher  than  the 
men's  heads,  and  so  as  to  leave  intervals  between  the 
bags  in  the  lower  rows,  through  which  the  men  can 
aim  and  fire  their  pieces.  (Fig.  28.)  Gabions  are  also 
used  for  a  similar  purpose.  The  gabions  are  placed 
in  pairs  upon  the  parapet  and  filled  with  earth,  each 
pair  being  separated  from  the  adjacent  pair  by  an 
interval  of  about  two  inches. 

A  contrivance  adopted  in  the  war  of  1861-5,  was 


INTERIOR   ARRANGEMEyXS   OF  A   FIELD   WORK,     127 

quite  effective  -for  the  same  purpose.  Skids  were 
placed  upon  the  parapet,  with  notches  cut  in  them. 
A  heavy  log  was  placed  on  the  skids,  occupying  a  po- 
sition parallel  to  the  interior  crest  and  just  in  contact 
with  the  superior  slope.  Notches  were  cut  in  the 
under  side  of  this  horizontal,  log  and  these  'were  used 
as  loop-holes.  The  openings  to  the  exterior  were 
made  as  small  as  possible,  and  in  some  cases  were 
protected  by  small  plates  of  boiler  iron  spiked  upon 
the  log.  When  exposed  to  artillery  fire,  earth  was 
banked  against  the  log. 

A  wooden  loop-hole  was  devised  by  Lieut.  King 
(now  Major)  of  the  United  States  Engineers,  which 
was  used  in  1864.  It  was  practically  a  wooden  hopper 
made  of  boards,  placed  upon  the  superior  slope  of  the 
parapet,  and  covered  with  earth.  The  splay  of  the 
sole  and  the  angle  of  the  cheeks  were  made  to  suit 
the  field  of  fire  required. 

The  exterior  orifice  of  a  loop-hole  for  musketry 
should  be  made  as  small  as  possible.  A  width  of 
hvo  inches  and  a  height  of  five,  is  sufficiently  large 
for  ordinary  purposes.  The  sides  are  sloped,  and  an 
inclination  given  to  the  bottom  and  top,  according  to 
the  field  of  fire  which  is  to  be  swept. 

Embrasures  are  sometimes  protected  in  a  manner 
similar  to  this  arrangement  for  loop-holes.  Timbers 
are  laid  across  the  embrasure,  covering  the  throat, 
leaving  only  room  for  the  muzzle  of  the  piece.     These 


128  FIELD  FORTIFICATIONS, 

timbers  are  then  covered  by  sand  bags,  by  fascines, 
etc.,  to  make  them  shot-proof.  Sometimes  the  em- 
brasure is  filled  in  with  sand  bags  or  fascines  to  mask- 
it,  these  things  being  quickly  removed  when  the  em- 
brasure is  needed  for  use. 

Thick  wooden  shutters,  made  bullet-proof,  and 
placed  on  vertical  axes,  and  iron  shutters  swung  on 
horizontal  axes,  have  both  been  used  to  close  the 
throat  of   the   embrasure. 

In  some  cases,  timber  supports  were  extended  back 
from  the  parapet  and  a  covering  of  timber  and  earth 
placed  upon  them,  protecting  the  gun  from  vertical 
and  plunging  fire.  A  gun  thus  sheltered  is  said  to 
be  case-mated. 

109.  Traverses. — The  traverses  constructed 
along  a  parapet  are  of  two  kinds,  viz.,  the  traverses 
built  to  afford  shelter  against  slant  and  enfilading 
fires,  and  those  built  as  a  protection  against  the  frag- 
ments of  bursting  shells. 

Traverses  may  be  built  at  the  same  time  that  the 
work  is  constructed,  or  they  may  not  be  built  until 
there  is  an  immediate  necessity  for  them. 

In  the  former  case,  their  construction  is  in  all 
things  similar  to  that  of  the  parapet,  viz.,  tracing, 
profiling  and  execution.  In  the  latter  case,  they  are 
generally  built  in  great  haste,  and  profiles  are  not 
used.  The  construction  is  of  the  simplest  kind,  hav- 
ing for  its  object  to  interpose  a  mass  of  earth  upon 


INTERIOR   ARRANGEMENTS    OF  A    FIELD   WORK,     129 

a  line  of  fire,  in  the  shortest  time  possible.  This  is 
done  by  piling  sand-bags  filled  with  earth  upon  the 
spot  to  be  occupied  by  the  traverse,  and  raising  there 
a  mass  thick  enough  and  high  enough  to  serve  the  end 
required.  Gabions  filled  with  earth  are  frequently  used 
for  the  same  purpose. 

The  top  of  a  traverse  is  usually  made  ridge-shaped, 
so  as  to  carry  away  the  rain  water  which  falls  upon  it. 
The  sides  of  the  traverse  are  sloped,  the  inclination  of 
the  slopes  being  the  same,  or  different,  according  to  the 
degree  of  exposure  of  the  traverse  to  the  enemy's  fire. 

The  traverse  shown  in  Fig.  40  is  an  example  of  a 

Fig.  40. 


traverse  built  to  shelter  the  men  on  the  banquette  from 
a  slant  or  enfilading  fire,  coming  in  the  direction  shown 
by  the.  arrow.  Its  top  is  made  ridge-shaped.  The 
side  towards  the  enemy  has  the  natural  slope  of  the 
earth  ;  the  opposite  side  is  made  steeper,  and  should 
be  revetted.  The  thickness  of  the  traverse  depends 
upon  its  exposure  to  the  enemy's  fire.      If  a  fire  can 


130 


FIELD   FORTIFICATIONS, 


be  brought  directly  upon  it,  it  should  have  the  same 
thickness  as  that  given  to  the  parapet. 

Its  height  and  length  depend  upon  the  amount  of 
banquette  and  terreplein  which  are  to  be  defiladed 
by  it. 

The  manner  in  which  this  traverse  is  joined  to  the 
parapet  is  shown  in  Fig.  41,  which  represents  its  plan. 

Fig.  41. 


The  slope  on  the  side  toward  the  enemy  is  shown, 
in  both  of  these  figures,  to  be  uniform.  This  is  not 
always  the  case.  The  portion  exposed  to  the  enemy's 
fire  is  given  the  natural  slope  of  the  earth  ;  but  below 
this  plane  of  fire,  the  slope  may  be  revetted,  and  made 
steeper. 

Instead  of  being  ridge-shaped,  the  traverses  are,  in 
many  cases,  made  with  a  cross  section  similar  to  that 
of  the  parapet. 

110.     Splinter-proof  traverses. — A    traverse 


INTERtOR   ARRANGEMEyTS   OF  A   FIELD  WORK.     131 

intended  to  be  used  only  as  a  protection  against  splin- 
ters and  the  fragments  of  shells  scattered  around  by 
their  explosion,  is  known  as  a  splinter-proof  tra- 
verse. 

Traverses  of  this  kind  are  not  made  so  thick,  nor 
so  high,  as  the  traverses  just  described.  Their  usual 
height  is  the  same  as  that  of  the  parapet.  Their  thick- 
ness at  the  base  is  from  seven  to  eight  feet.  Their 
length  varies,  being  in  some  cases  only  ten  feet,  and 
in  others  as  much  as  sixteen  feet. 

As  a  rule,  a  traverse  of  this  kind  is  not  joined  to 
the  parapet,  but  is  separated  from  it  by  a  narrow  pas- 
sage which  can  be  used  by  the  men  to  pass  from  one 
side  of  the  traverse  to  the  other. 

Fig.  42. 


A  splinter-proof  traverse  (Fig.  42)  is  usually  con- 
structed as  follows  : 

A  rectangular  space  is  marked  upon  the  ground 
for  the  base  of  the  traverse.     A  row  of  gabions  is  then 


132  FIELD  FORTIFICATIONS. 

placed  in  juxtaposition  along  the  line  representing  the 
base  of  the  traverse,  and  given  a  slope  inwards,  either 
by  setting  the  gabions  on  a  slightly  inclined  excava- 
tion in  the  ground,  or  by  raising  the  outer  edges  by 
means  of  fascines  laid  along  on  the  ground. 

The  gabions  are  then  filled  with  earth,  and  also  the 
interior  space  enclosed  by  them. 

When  the  earth  has  risen  above  the  top  of  the  gab- 
ions, two  rows  of  fascines  are  laid  upon  the  top  of  the 
gabions  to  form  a  base  for  a  second  row  of  gabions. 
This  second  row  is  then  filled  with  earth,  and  the  pro- 
cess of  filling  with  earth  goes  on  until  the  earth  rises 
high  enough.  The  top  is  rounded  off  or  made  ridge- 
shaped,  and  the  traverse  is  completed. 

The  same  method  may  be  used  for  the  construc- 
tion of  traverses  required  for  defilade,  when  there  is 
a  pressing  emergency  for  them. 

Splinter-proof  traverses  are  placed  between  the  guns 
along  a  line  of  parapet  which  is  exposed  only  to  a 
direct  fire  from  the  enemy,  and  are  only  intended 
to  confine  the  effects  of  bursting  projectiles  to  a  limi- 
ted space. 

They  are  usually  constructed  only  when  there  is  a 
necessity  for  them  and  then  hastily.  Gabions,  sand 
bags,  fascines,  or  any  of  the  materials  used  for  revet- 
ments may  be  employed  in  their  construction. 

111.  Platforms. — A  field  gun  or  any  piece  of 
artillery,   after    repeated   discharges  in  the  same  direc- 


INTERIOR   ARRANGEMENTS   OF  A   FIELD  WORK.     133 

tion,  soon  wears  the  ground  under  its  wheels  into 
ruts^  if  these  wheels  rest  upon  the  ground.  The 
result  of  this  is  to  lower  the  piece  and  to  increase  the 
difficulties  of  handling  the  gun. 

By  resting  the  wheels  upon  a  hard  and  smooth  sur- 
face this  trouble  is  avoided.  This  surface  is  furnished, 
in  field  works,  by  -wooden  platforms  upon  which 
the  wheels  of  the  gun-carriages  rest.  The  platform  is 
made  rectangular  or  trapezoidal  in  plan,  and  large 
enough  for  the  service  of  the  gun. 

A  field  gun  should  have  a  platform  at  least  ten  feet 
wide  in  front,  and  fifteen  feet  long.  A  siege  gun  would 
require  a  platform  fourteen  feet  wide  and  eighteen  feet 
long. 

The  dimensions,  bill  of  materials,  and  method  of 
constructing  platforms,  are  laid  down  in  the  manuals 
of  engineering  and  ordnance,  and  to  these  works  the 
student  is  referred  for  the  details  of  such  construction. 

A  temporary  wooden  platform,  which  can  be  quickly 
constructed  and  can  be  used  until  a  better  one  is  pro- 
vided, may  be  made  as  follows  : 

The  earth  upon  which  the  platform  is  to  rest 
should  be  thoroughly  rammed.  Trenches,  as  many  as 
there  are  sleepers,  are  then  dug  parallel  to  the  direc- 
trix of  the  embrasure,  or  perpendicular  to  the  interior 
crest  in  case  of  a  barbette.  In  these  trenches  sleepers 
are  bedded,  so  as  to  have  their  rear  ends  raised  about 
six  inches  above  the  front  ends.     Planks,  at  least  three 


134  FIELD   FORTIFICATIONS. 

inches  thick,  are  nailed  or  spiked  transversely  upon 
these  sleepers.  This  practically  completes  the  plat- 
form. 

A  piece  of  timber,  at  least  six  inches  in  diameter, 
is  spiked  to  the  front  part  of  the  platform  in  such  a 
position  that  when  the  wheels  of  the  carriage  rest 
against  it,  they  will  not  touch  the  interior  slope  of  the 
parapet.  This  piece  against  which  the  wheels  rest  is 
called  a  hurter. 

It  is  frequently  advisable  to  spike  timbers  along 
the  sides,  to  act  as  guards  and  prevent  the  wheels  of 
the  carriage  from  running  off  the  platform.  These 
pieces,  termed  side-rails,  are  also  useful  to  assist  in 
holding  the  planks  in  place. 

The  raising  of  the  sleepers  at  the  rear  ends  gives  to 
the  platform  an  inclination  to  the  front,  which  assists 
in  running  the  gun  *^in  battery"  after  it  has  been 
loaded,  and  assists  in  checking  the  recoil  of  the  piece 
when  it  is  fired. 

The  number  of  sleepers  used  for  the  platform  de- 
pends upon  the  size  of  the  platform  and  the  abundance 
of  timber  in  the  vicinity  of  the  work. 

A  sleeper  is  laid  directly  under  the  middle  line  of 
the  platform.  The  others  are  laid  parallel  to  this  one, 
on  either  side,  and  at  equal  distances  apart.  In 
emergencies,  and  where  timber  is  scarce,  only  three 
sleepers  may  be  used  ;  a  middle  one,  and  two  outside 
ones,   the  latter  being  placed  so  as  to  be  directly  un- 


INTERIOR   ARRANGEMENTS   OF  A   FIELD  WORK,    135 

der  the  wheels  of  the  carriage  when  the  gun  is  '^in 
battery."  If  timber  is  plentiful,  they  are  placed  not 
more  than  two  feet  apart,  from  centre  to  centre,  and 
sometimes  even  in  juxtaposition.  At  the  outer  end 
of  each  sleeper  a  stout  wooden  picket  is  driven  to 
keep  the  platform  steady. 

In  the  Franco- Prussian  war  of  1870-1,  the  Prus- 
'  sians  made  use  of  a  device  which  was  sent  into  the  field 
with  each  siege  gun.  This  device  consisted  of  two  in- 
clined planes  of  stout  plank,  faced  with  sheet  iron,  with 
a  rise  of  one  on  six,  and  from  eight  to  nine  feet  long. 
An  ordinary  wooden  platform,  or  merely  a  platform  of 
planks,  was  laid,  and  on  it  and  under  the  wheels  were 
placed  these  inclined  planes. 


f/? 


II.  Shelters  for  the  troops,  etc. 

112.  Shelters, — An  efficient  defence  of  a  field 
work  is  greatly  aided  by  shelters  arranged  for  the 
men  and  the  stores,  so  that  the  men  can  rest  in  them, 
and  the  stores  can  be  kept  safe  from  the  enemy's  fire. 

The  shelters  generally  used  are  known  as  bomb- 
proofs,  and  splinter-proofs,  which  differ  from  each 
other  only  in  capacity  and  strength. 

Bomb-proofs  must  be  strong  enough  to  resist  the 
effects  both  of  the  impact  and  of  the  explosion  of  the 
projectiles  which  strike  them.  They  should  be  roomy, 
and  when  used  by  the  men  should  be  well  ventilated. 

Splinter-proofs  are  so  placed  that  they  are  not  ex- 


1-^n  FIKLD   FORTIFICATIONS, 

posed  to  tlie  impiict  of  projectiles.  They  are  liable  to 
be  struck  by  fragments  of  shells,  or  splinters  knocked 
off  by  the  impact  of  a  projectile,  and  are  therefore 
made  only  strong  enough  to  resist  the  effects  of  the 
flying  fragments  and  splinters  produced  by  shells 
bursting,  or  by  projectiles  striking  near  them. 

113.  Construction  of  bomb-proofs. — Bomb- 
proofs  may  be  built  during  the  construction  of  the 
parapets,  or  after  the  parapets  are  finished.  The  latter 
is  the  more  usual  method. 

The  position  in  a  field  work  occupied  by  a  bomb- 
proof depends  upon  the  size  of  the  work,  the  kind  of 
trace,  degree  of  exposure  of  the  interior  of  the  work, 
the  convenience  of  the  position,  etc.  Hence,  bomb- 
proofs  are  sometimes  placed  under  the  parapet ;  some- 
times in  the  gorge  of  a  half-closed  work;    sometimes 

^""--.^  Fig.  43. 


in  the  middle  of   the  parade,  etc.;  the  position  being 
determined  by  the  circumstances  of  each  case. 

Fig.  43  represents  a  cross  section  of  a   bon^b-proof 


INTERIOR  ARRANGEMENTS   OF  A   FIELD  WORK.     137 

into  which  the  men  can  retire  and  be  safe  from  the 
effects  of  a  direct  plunging  or  curved  fire. 

The  construction  of  this  bomb-proof  was  as  fol- 
lows :  A  row  of  vertical  posts,  in  contact  or  at  short 
distances  apart,  were  framed  into  ground  sills,  or  set 
into  the  ground,  at  the  bottom  of  the  trench,  along 
a  line  far  enough  away  from  the  side  of  the  trench 
next  to  the  enemy's  fire  to  allow  room  for  a  man  to 
recline  at  full  length  or  occupy  a  comfortable  posi- 
tion. These  posts  were  then  capped  with  stout  tim- 
bers. 

A  second  row  of  posts  was  placed,  either  vertical 
or  inclined,  against  the  side  of  the  trench,  and  this 
row  was  capped  in  a  similar  manner.  Cross  timbers 
were  laid  in  juxtaposition  upon  these  capping  timbers, 
and  then  covered  with  planks,  fascines,  etc.,  to  form 
a  tight  roof. 

This  roof,  when  thus  formed,  was  covered  with 
sufficient  earth  to  make  it  proof  against  the  effects 
produced  by  the  impact  of  projectiles,  or  the  effects 
resulting  from  their  explosion.  A  thickness  of  five 
feet  of  earth,  in  a  vertical  direction,  is  usually  con- 
sidered sufficient  to  make  a  roof  proof  against  the 
effects  produced  by  projectiles  of  field  guns. 

Ingress  and  egress  of  the  men  using  the  bomb- 
proof may  be  facilitated  by  cutting  steps  into  the 
side  of  the  trench,  as  shown  in  the  figure.  The  part 
of  the  bomb-proof    resting    against  the  side   of    the 


138  FIELD  FORTIFICATIONS. 

trench  should  be  revetted  by  a  covering  of  plank,  fas- 
cines, or  other  suitable  material,  to  keep  the  shelter 
dry,  and  to  make  it  more  comfortable.  Guard  beds 
should  be  constructed,  when  the  bomb-proof  is  wide 
enough,  so  that  the  men  can  lie  down  at  full  length  ; 
if  not  wide  enough,  benches  can  be  made  which  will 
allow  the  men  to  assume  easy  positions. 

A  construction  like  that  shown  in  Fig.  43,  can 
easily  be  placed  under  the  banquette,  when  the  com- 
mand is  9|  feet,  the  banquette  in  this  case  serving 
as  the  top  of  the  bomb-proof. 

114.  Blindages. — Any  construction  used  in 
field  works  which  has  for  its  object  the  protection 
of  the  men  and  material  against  the  effects  of  artillery 
lire  from  overhead,  is  termed  a  blindage.  The  pre- 
ceding construction,  therefore,  is  a  blindage. 

115.  Splinter-proofs. — Shelters  which  are  not 
exposed  to  the  impact  of  the  projectiles  of  the  enemy, 
need  not  be  so  strong  as  the  bomb-proof.  It  will  be 
sufficient  if  they  are  proof  against  the  splinters  and 
fragments  of  shells,  produced  by  the  enemy's  fire. 

Shelters  of  this  kind  are  usually  constructed  in 
inclined  positions.  (Fig.  44).  They  are  made  by  plac- 
ing strong  timbers,  or  bars  of  railroad  iron,  in  an  in- 
clined position  against  the  surface  to  be  protected,  and 
in  juxtaposition,  and  then  covering  them  with  earth 
sufficient  to  make  the  interior  safe  against  the  frag- 
ments which  may  strike  the  shelter. 


INTERIOR   ARRANGEMENTS   OF  A   FIELD   WORK,     139 

The  inclination  of  the  timbers  will  be  equal  to,  or 
less,  than  the  natural  slope  of  the  earth  thrown  against 
them.      It  is  well  to  cover  the  pieces  with  raw-hides 

Fig.  44. 


or  tarpaulins  before  the  earth  is  thrown  against 
them,   to  make  the  shelter  water-tight. 

A  thickness  of  two  feet  of  earth  is  sufficient  to 
resist  the  fragments  of  shells  fired  from  field  guns. 
In  many  cases  the  earth  is  placed  upon  the  shelter  by 
piling  sand  bags  filled  with  earth  against  it. 

Entrance  to  the  shelter  is  provided  for  by  openings 
at  the  ends,  sometimes  by  openings  left  at  intervals. 

Splinter-proofs,  from  their  nature,  are  placed  in 
those  situations  where  they  are  not  exposed  to  a  direct 
fire.  They  are  much  used  to  protect  doors,  entrances, 
etc.,  which  are  exposed  to  the  effects  of  bursting 
shells  ;  to  protect  vertical  walls  liable  to  injury  from 
the  same  cause  ;  etc. 

116.  Powder     magazines,    etc.— Shelters    in 


140 


FIELD  FORTIFICATIONS. 


which  the  ammunition  and  other  stores  can  be  placed 
and  kept  safe  from  the  effects  of  the  enemy's  fire,  are 
equally  as  important  as  the  shelters  for  the  men. 
The  most  important  of  these  are  the  powder  maga- 
zines, or  those  shelters  intended  for  the  storage  of 
the  ammunition. 

The  rules  given  for  the  construction  and  location 
of  bomb-proof  shelters  for  men,  apply  equally  to  shel- 
ters of  this  class.  The  only  difference  in  construction 
is  in  the  size  of  the  shelter,  it  being  much  smaller, 
as  a  rule,  than  that  required  for  the  use  of  troops. 

Large  magazines  are  not  constructed  in  ordinary 
field  works.  They  take  up  too  much  room,  and  even 
the   best   of  them  are  but  poor  places   in   which   to 

Fig.  45. 


store  ammunition  for  any  length  of  time.  The  usual 
method  adopted  is  to  construct  as  many  service 
magazines  as  may  be  necessary,  near  the  guns  to 
be  served  by    them,    making   them    large    enough    to 


INTERIOR   ARRANGEMENTS   OF  A   FIELD  WORK.    141 

contain  the  amount  required  for  a  definite  service  of 
the  gun  or  guns  to  which   they  belong. 

117.  Service  magazines. — Magazines  of  this 
kind  are  oftentimes  built  in  the  adjacent  traverses 
(Fig.  45)  if  there  be  any  ;  generally  under  the  parapet 
near  the  guns  ;  and  sometimes  under  the  barbettes. 

Fig.  46. 


The  conditions  to  be  observed  in  locating  and  con- 
structing a  powder  magazine  are  that  it  shall  be  con- 
veniently placed  ;  shall  not  be  exposed  to  a  direct  lire 


142  FIELD  FORTIFWATWKS. 

of  the  enemy  ;  be  made  bomb-proof  ;  be  well  drained  ; 
and  if  practicable,  be  well  ventilated. 

A  service  magazine  may  be  entirely  above  the  sur- 
face of  the  ground  (Pig.  45)  or  partly  or  wholly 
under  the  ground  (Fig.  46). 

The  construction  of  a  service  magazine,  in  which 
the  magazine  and  passage-way  are  lined  with  wooden 
frames,  is  represented  in  Fig.  46. 

The  frames  are  made  of  timbers  or  scantlings  of 
the  proper  dimensions,  each  frame  consisting  of  two 
uprights,  called  stanchions,  a  ground  sill,  and  a  cap. 
The  interior  dimensions  of  the  frame  are  the  same 
as  that  of  the  magazine,  or  six  feet  high  and  six  feet 
wide,  the  least  dimensions  given,  when  practicable,  to 
the  width  and  height  of  the  interior  space. 

The  frames  are  placed  upright,  about  three  feet 
apart,  and  in  the  position  which  they  are  to  occupy. 
Their  tops  and  sides  are  then  planked  over ;  this  plank- 
ing is  called  the  sheeting. 

The  bottom  of  the  excavation  is  sloped  from  the 
sides  to  the  middle,  and  from  the  rear  to  the  front,  to 
allow  all  water  leaking  through  the  magazine  to  col- 
lect in  a  shallow  trench  made  along  the  middle  line, 
and  to  run  off  into  a  drain  prepared  to  receive  it,  or 
into  a  dry  well  dug  near  the  entrance.  The  ground 
sills  are  then  floored  with  boards. 

Great  care  should  be  taken  to  make  the  top  water- 
tight, before  the  earth  is  placed  upon  it.     This  done. 


INTERIOR   ARRANGEMENTS   OF  A    FIELD    WORK,    143 

it  is  covered  with  several  feet  of  earth  depending  upon 
the  degree  of  exposure  to  which  it  is  subjected. 

The  plan,  and  horizontal  section  of  the  magazine 
and  entrance,  made  by  the  plane  A  B  j  ^^^  the  eleva- 
tion, and  section  by  the  vertical  plane,  C  D^  ^^^  shown 
in  Fig.  46. 

The  entrance  to  the  magazine  should  be  closed  by 
a  stout  door,  and  the  approach  to  it  should  be  protected 
by  a  splinter-proof.  If  field  artillery  is  employed  to 
defend  the  work,  the  limber  boxes  are  taken  off  and 
placed  within  the  magazines. 

118.  Shelter  for  guns,  etc. — Shelters  are  fre- 
quently provided  for  guns,  implements,  etc. 

The  thing  to  be  sheltered,  its  dimensions,  and  its 
uses,  will  regulate  the  details  of  construction  of  the 
shelter.  The  rules  applicable  for  the  shelter  just  de- 
scribed, apply  equally  to  shelters  of  this  class. 

119.  Materials  used  in  the  construction 
of  shelters. — Timber  has  been  considered  to  be  the 
material  used  in  the  construction  of  the  above  shelters. 
This  material  is  so  abundant  in  the  United  States  chat 
it  can  almost  always  be  found  in  quantities  near  the 
work,  and  can  be  obtained  quickly.  It  will  therefore 
be  the  material  chiefly  used  in  temporary  fortifications. 

ISTo  better  material  can  be  used  for  the  transverse 
pieces  of  these  shelters  than  railroad  iron,  if  it  can  be 
obtained.  The  form  of  the  rails  allows  the  pieces  to  be 
placed  in  juxtaposition  without  delay,  and  the  strengch 


144 


FIELD   FORTIFICATIONS, 


of  the  iron  makes  the  roof  more  able  to  resist  the  shocks 
of  the  projectiles,  and  makes  the  structure  more  dur- 
able in  its  character. 

120.  Bomb-proof  shelters  used  in  the  de- 
fences of  Washington. — The  field  works  employed 
to  defend  AVashingcon,  in  the  war  of  1861-5,  are  fine 
examples  of  temporary  fortifications.  They  were  in 
the  beginning,  constructed  according  to  the  rules  laid 
down  for  temporary  works.  But  as  time  passed,  and 
their  great  importance  was  recognized,  the  dimensions 
of  the  parts  of  the  different  works  were  increased,  and 
the  interior  arrangements  so  improved  that  the  works 
passed  beyond  the  limits  laid  down  for  field  works,  and 
approximated  in  profile  and  in  the  interior  arrange- 
ments to  permanent  fortifications. 

The  section  of  a  bomb-proof,  shown  in  Fig.  47, 
gives  a  type  of  the  shelters  built  for  the   men. 

Fig.  47. 


Its  construction  differs  but  slightly  from  those 
already  described.  It  is  larger,  and  is  provided  with  a 
banquette  by  means  of  which  a  musketry  fire  could  be 
delivered  over  the  top  of  the  shelter,  if  required. 


INTERIOR   ARRANGEMENTS   OF  A   FIELD   WORK.    1^5 


The  shelter  represented  by  it  was  located  near  the 
middle  of  the  parade. 

121.  Powder  magazines  used  in  the  de- 
fences of  Washington.— The  powder  magazines  at 
first  used  were  built  like  that  described  in  art.  117. 
They  were  soon  replaced  by  other  constructions,  of  which 
the  section  shown  in  Fig.  48.  represents  the  type. 

Fig.  48, 


The  new  magazines  were  made  stronger  and  more 
durable,  were  better  drained,  and  were  well  ventilated ; 
in  all  of  which  qualities  the  older  ones  were  deficient. 

This  particular  example  shown  in  Fig.  48,  was  built 
under  a  traverse. 

The  essential  difference  between  this  particular 
magazine  and  those  usually  constructed,  is  the  employ- 
ment of  an  air-chamber  to  prevent  the  accumulation 
of  moisture  which  otherwise  would  take  place  upon 
the  inner  side  of  the  magazine.  This  chamber  was 
constructed  by  placing  logs  in  an  inclined  position 
against  the  sides  of  the  magazine,  framing  them  into 
a  ground-sill,  and  bracing  them  at  the  middle.     Small 


146  FIELD   FORTIFICATIONS, 

poles,  from  two  to  four  inches  in  diameter,  were  laid 
against  these  inclined  pieces  to  hold  up  the  earth 
thrown  against  them.  Ventilators  connected  the  in- 
terior of  the  magazine  with  the  air  chamber,  and  the 
air  chamber  with  the  outside. 

Particular  attention  was  paid  to  making  the  roof 
water-tight  in  all  the  magazines. 

Whenever  it  was  practicable,  the  drainage  was  car- 
ried to  the  main  ditch  of  the  work. 

On  the  sides  of  a  magazine  exposed  to  the  enemy's 
fire,  the  thickness  of  earth  was  made  such  as  to  meas- 
ure at  least  ten  feet  from  the  woodwork  of  the  maga- 
zine to  the  exterior,  along  a  line  making  an  angle  of 
thirty  degrees  with  the  horizontal. 

Magazines  of  the  dimensions  of  those  built  in  the 
defences  of  Washington  are  not  usually  required,  nor 
are  they  built  in  ordinary  field  works.  But  when  a 
field  work  is  to  be  occupied  for  some  time,  and  a  large 
quantity  of  ammunition  is  to  be  stored  in  temporary 
magazines,  the  principles  governing  the  construction 
of  the  magazines  should,  as  far  as  practicable,  be  in 
accordance  with  those  illustrated  by  this  example. 

122.  Position  given  to  the  shelters,  etc.— 
No  absolute  rule,  or  set  of  rules,  can  be  made  which 
will  apply  to  all  cases  in  practice.  Each  particular 
work  must  be  considered  by  itself  and  in  connection 
with  its  surroundings.  Interior  arrangements  ex- 
tremely   necessary    in  one   particular   work    might   be 


INTERIOR   ARRANGEMENTS    OF  A    FIELD   WORK.     147 

useless  in  another ;  the  positions  occupied  by  these 
arrangements  in  one  woric  might  be  the  worst  places 
for  them  in  a  work  of  another  kind,  or  in  a  work 
situated  in  a  different  locality. 

The    plan    shown    in    Fig.    49,    representing    the 


Fig.  49. 


northern  half  of  a  redoubt  used  at  the  seige  of  Pe- 
tersburg, in  Virginia,  in  1864,  may  be  taken  to  illus- 
trate the  way  in  which  the  interior  arrangements  are 
sometimes  located. 

The  trace  of  the  redoubt  was  an  irregular  penta- 
gon, and  the  portion  shown  in  the  figure  was  that 
part  toward  the  enemy. 


148  FIELD   FORTIFICATIONS, 

III.  Communications,  barriers,  etc. 

123.  Communications. — The  defenders  of  a 
closed  work  must  have  arrangements  made  by  means 
of  which  they  can  enter  or  go  out  of  the  work  when 
necessary.  In  case  of  continued  lines,  arrangements 
should  be  provided  by  means  of  which  the  defenders 
can  make  sorties. 

The  method  adopted  is  to  leave  openings  in  the 
parapet,  through  which  passages  are  built  leading  to 
the  outside  of  the  work.  These  openings  made  in  a 
parapet  are  necessarily  weak  points  of  a  work.  As  a 
consequence,  they  should  be  placed  where  they  will 
be  the  least  exposed,  and  can  be  most  easily  guarded. 
No  greater  number  should  be  constructed  than  the 
actual  necessities  of  the  work  demand. 

In  redoubts,  the  outlets  are  on  the  sides  least  ex- 
posed to  attack  ;  in  half -closed  works,  they  are  placed 
near  the  middl-e  of  the  gorge  ;  in  forts,  they  are 
usually  placed  near  the  re-entrants. 

A  passage  for  the  use  only  of  infantry  should  not, 
as  a  general  thing,  be  less  than  six  feet  wide  ;  for 
artillery,  not  less  than  ten  feet  wide  ;  for  sorties,  the 
outlets  in  continued  lines  should  be  at  least  fifty 
yards  wide. 

124.  Masks  opposite  the  outlets. — The  out- 
let should  be  masked  in  some  way  to  prevent  an 
enemy,  on  the  same  side  of  the  work  with  the  outlet. 


INTERIOR   ARRANGEMENTS    OF  A   FIELD   WORK.    149 

seeing  into  the  enclosed  space.  This  is  usually  done 
by  placing  a  traverse  inside  of  the  work  and  oppo- 
site the  outlet  (Fig.  50). 


Fig.  50. 


The  traverse  has,  ordinarily,  the  same  height  as 
the  parapet  behind  which  it  is  placed,  and  a  similar 
profile. 

Eoom  sufficient  for  a  road-way,  is  left  between 
the  foot  of  the  exterior  slope  of  the  traverse  and  the 
foot  of  the  banquette  slope  of  the  parapet.  The  trav- 
erse must  be  long  enough  to  intercept  all  projectiles 
which  an  enemy  on  the  outside  can  fire  through  the 
opening  in  the  parapet.  Its  length  will  therefore  de- 
pend upon  the  width  of  the  outlet  and  the  thickness 
of  the  parapet. 

The  limiting  plane  of  fire,  above  which  a  direct 
fire   may  be  neglected,  is  taken  to  be  five  feet  above 


150  FIELD   FORTIFWATTONS, 

the  ground  on  which  the  man  stands.  The  intersec- 
tion of  this  plane  of  fire  with  the  sides  of  the  outlet 
should  be  determined,  and  the  extreme  lines  of  fire 
drawn.  Let  the  dotted  lines,  through  c  and  g,  be  the 
extreme  lines  of  fire.  If  the  exterior  crest  of  the 
traverse  rests  on  these  two  lines,  the  traverse  will  in- 
tercept all  fire  from  the  outside  coming  through  the 
opening  in  the  parapet. 

When  the  height  of  the  parapet  is  eight  feet,  it 
will  be  suflficiently  accurate  for  all  practical  purposes 
to  take  the  horizontal  plane  passing  through  the  exter- 
ior crest  as  the  limiting  plane  of  fire,  and  to  use  the 
horizontal  lines  passing  through  c  and  g,  shown  dotted 
in  the  figure,  as  the  extreme  lines  of  fire. 

The  more  accurate  method  would  be  to  determine 
these  extreme  lines,  by  passing  a  plane  five  feet  above 
the  ground,  and  finding  its  intersection  with  the  sides 
of  the  outlet,  and  with  the  exterior  and  interior  slopes 
of  the  parapet.  Join,  by  a  straight  line,  the  point 
of  intersection  of  the  line  cut  from  the  exterior 
slope  and  either  of  the  lines  cut  from  the  sides 
of  the  outlet,  with  the  point  of  intersection  of  the 
line  cut  from  the  opposite  side  of  the  outlet  and 
the  line  cut  from  the  interior  slope.  This  line,  thus 
drawn,  will  be  one  of  the  limiting  lines.  In  a  simi- 
lar way,  the  other  line  could  be  obtained. 

125.  The  length  of  the  traverse  may  be  shortened 
by  turning  back  the  interior  crest  at  right  angles  to  its 


INTERIOR   ARRANGEMENTS    OF  A   FIELD   WORK,     151 

general  direction,  and  extending  it  as  far  as  the  crest 
of  the  banquette  (B  B^  Fig.  50). 

Instead  of  having  a  road  along  its  entire  front, 
the  traverse  is  sometimes  joined  to  the  parapet  on  one 
side  of  the  opening,  as  shown  by  the  dotted  lines  h  d 
and  e  /,  in  Fig.  50. 

Sometimes,  it  is  necessary  to  dispense  with  a  tra- 
verse in  the  interior.  Especially  is  this  the  case  where 
the  outlet  is  a  very  wide  one,  and  the  interior  space 
quite  limited. 

The  method  adopted  to  mask  the  interior  of  the 
work  in  this  latter  case,  is  to  place  the  traverse  op- 
posite the  outlet  on  the  outside,  and  beyond  the  ditch. 
(Fig.  51). 


Interior  Crest 


Fig.  51. 


The  traverse  in  this  case  is  usually  broken,  gener- 
ally a  redan  in  trace,  with  the  profile  of  a  parapet,  but 
commanded  by  the  parapet  in  rear. 

125.  Barriers. — The  outlets  are  usually  ar- 
ranged   so  that  they  can    be  quickly  closed,  to   guard 


152 


fieij  d  fo  r  t I  fig  a  tions. 


against  surprise.     The    means  used   is   a  gate,    techni- 
cally termed  a  barrier. 

The  gate  is  made  with  two  leaves,  hanging  on  posts 
by  hinges,  and  made  to  open  outwards. 

The  frame  of  each  leaf  is  composed  of  two  uprights, 
called  stiles  j  two  cross  pieces,  one  at  the  top  and  the 
other  at  the  bottom,  called  rails*  and  a  diagonal 
brace,  called  a  s-winging  bar. 

The  leaf  of  the  barrier  may  be  made  open,  by  spik- 
ing stout  upright  pieces,  with  intervals  between  them, 
to  the  pieces  of  the  frame ;  or  it  may  be  made  solid, 
forming  what  is  known  as  a  bullet-proof  gate. 
(Fig.  52). 

Fig.  52. 


Since  the  gate  must  be  strong,  the  leaves  of  it  are 
necessarily  very  heavy.  The  leaves  must  be  hung 
upon  stout  posts,  firmly  braced  into  the  ground,  to  sus- 
tain the  great  weight  of  the  gate. 

The  top  rails  of  all  barriers  should  not  be  less  than 
six  feet  above  the  ground. 


INTERIOR    ARRANGEMEXTS    OF  A    FIELD  WORK,     153 

111  the  barriers  with  open  leaves,  the  vertical  pieces 
are  usually  extended  from  eighteen  inches  to  two  feet 
above  the  top  rails,  and  their  upper  ends  sharpened. 

In  those  which  are  solid,  ifc  is  usual  to  arrange  some 
obstruction  upon  the  top  rail,  such  as  sharp  pointed 
.spikes,  broken  glass,  etc.,  to  interfere  with  persons 
climbing  over  the  top.  It  is  usual  to  provide  aper- 
tures in  the  leaves,  through  which  the  men  can  fire 
upon  the  ground  on  the  outside. 

127.     Bridges. — When   the  ditch  has  been  com- 
pleted along  that  part  of  the  work  in  front  of  the  out-  " 
let,  it  is  usual  to  carry  the  roadway  across  the  ditch 
by  means  of  a  bridge. 

The  ditches  of  field  works  are,  as  a  rule,  quite  nar- 
row, and  the  bridges  used  to  span  them  are  very  sim- 
ple constructions. 

A  common  method  of  building  the  bridge  is  to 
lay  three  or  more  sleepers  across  the  ditch,  and  cover 
them  with  planks  laid  transversely.  If  the  span  is 
sufficient  to  require  intermediate  supports,  these  are 
obtained  by  using  trestles  placed  in  the  ditch. 

A  bridge  built  in  this  way  can  be  quickly  re- 
moved and  speedily  re-built,  if  there  be  any  necessity 
for  it. 

Hand-books  on  military  engineering  describe  a 
number  of  bridge  constructions  for  use  in  fortifica- 
cations.  These  bridges  are  all  arranged  so  as  to  ad- 
mit of  communication   across   the  ditch   being   inter- 


154  FIELD   FORTIFICATIONS. 

riipted   at    pleasure,    and    are   either  draw   or  rolling 
bridges. 

The  draw-bridges  are  usually  made  with  a  leaf  to 
revolve  around  a  horizontal  axis,  the  leaf  usually  be- 
ing raised  to  a  vertical  position  when  the  communi- 
cation is  interrupted.  The  rolling  bridges  are  ar- 
ranged to  be  pushed  out  from  the  work,  and  drawn 
back  into  it.  Bridges  of  this  class,  known  as  mova- 
ble bridges,  are  useful  to  guard  against  surprise,  to 
prevent  stragglers  from  entering,  and  to  keep  the  gar- 
rison in,  the  work.  As  a  defence  against  an  assault 
of  a  field  work,  they  are  of  but  little  value. 

The  best  method,  is  to  have  no .  ditch  in  front  of 
an  outlet,  but  let  the  roadway  be  on  the  natural  surface 
of  the  ground. 

128.  Raznps. — The  short  roads  used  in  fortifica- 
tions to  ascend  from  one  level  to  another,  are  termed 
ramps. 

The  width  of  a  ramp  depends  upon  its  use,  fol- 
lowing the  rule  laid  down  for  the  width  of  passages. 
A  width  of  six  feet  for  infantry,  and  of  ten  feet  for 
artillery,  are  the  widths  generally  used. 

The  inclination  of  the  ramp  may  be  as  great  as 
one  on  six,  and  as  little  as  one  on  fifteen,  depending 
upon  the  difference  of  level  between  the  top  and  bot- 
tom. The  side  slopes  are  of  earth  with  its  natural 
slope. 

The    ramps  in   a  work  should   be   placed   in   posi- 


INTERIOR   ARRANGEMENTS   OF  A    FIELD  WORK.     155 

tions  where  they  will  not  be  in  the  way,  nor  occupy 
room  which  may  be  required  for  other  purposes. 

Steps  or  stairways  are  sometimes  used  instead  of 
ramps.  The  rule  for  them  is  that  the  breadth  of 
each  step,  called  the  tread,  shall  be  at  least  twelve 
inches,  and  the  height  of  the  step,  known  as  the 
rise,  shall  be  about  eight  inches. 

They  are  substituted  for  ramps  in  those  places 
where  there  is  not  sufficient  room  for  the  ramp. 

IV.  Arrangements  Intended  for  the  Comfort 
and  Health  of  a  Garrison. 

129.  Nature  of  the  arrangements. — A  garri- 
son compelled  to  live  within  an  enclosed  space  like  a 
field  work,  should  be  provided  with  all  the  arrange- 
ments which  are  necessary  for  the  health  and  for  the 
comfort  of  the  men,  consistent  with  surrounding 
circumstances. 

The  arrangements  essential  to  the  health  and 
comfort  of  the  men  include  those  intended  to  pro- 
tect them  from  the  weather,  to  provide  for  their 
support,  and  to  supply  their  necessities. 

The  principal  arrangements  are  the  tents,  huts, 
or  shelters  in  which  the  men  are  sheltered ;  the 
guard-houses,  and  rooms  for  those  on  duty ;  the 
kitchens  and  bake-ovens  in  which  the  food  is  pre- 
pared ;  the  sinks  or  privies,  and  the  places  provided 
for  the  men  for  washing  themselves  and  their  cloth- 


150  FIELD   FORTIFTCATIONS. 

ing  ;  the  hospitals  for  the  sick  ;  etc..  Wells,  or  means 
of  providing  the  garrison  with  a  supply  of  good 
drinking  water,  form  no  unimportant  part  of  the 
arrangements  necessary  for  the  comfort  as  well  as  the 
health  of  a  garrison. 

The  limits  of  this  book  will  not  admit  of  a  dis- 
cussion, nor  even  a  reference  to  the  various  divisions, 
of  this  important  section  of  the  interior  arrangements 
of  a  field  work. 

These  arrangements  are  second  only  to  those  re- 
quired for  actual  defence,  and  in  many  cases  they 
are  equal,  as  the  defence  of  the  work  in  a  great 
measure  depends  upon   them. 

The  only  rule  that  can  be  laid  down  is  to  make 
all  these  arrangements  of  a  temporary  character,  and 
to  place  them  so  that  they  can  be  removed,  at  a 
moment's  notice,  out  of  the  way  of  any  interference 
with  an  active  defence  of  the  fortification. 

V.  Other  kinds  of  Interior  Arrangements. 

130.    Secondary    interior    arrangements. — 

Besides  the  interior  arrangements  which  have  been 
described,  or  mentioned,  there  are  others  which  are 
secondary  in  their  nature.  These  are  the  arrange- 
ments which  are  to  be  used  under  certain  contingen- 
cies, or  in  cases  of  emergency.  An  example,  would 
be  a  defence  placed   within  a  field  work,    which  defence 


INTERIOR   ARRANGEMENTS   OF  A   FIELD  WORK,     157 

can  be  used  only  when  the  main  work  is  no  longer 
defensible,  etc. 

131.  Block-houses. — It  is  frequently  the  case 
that  a  separate  fortification  is  constructed,  lying  en- 
tirely within  a  work  exterior  to  it,  into  which  a  gar- 
rison can  retire  and  protract  their  resistance,  even 
after  the  outer  fortification  has  been  taken,  or  has 
been  made  unfit  for  further  defence. 

If  this  interior  work  is  a  line  of  earthern  para- 
pet, it  is  called  a  retrenchment  j  if  it  is  a  defen- 
sible building,  it  is  termed  a  keep. 

The  term,  keep,  is  also  applied  to  a  work  which  is 
entirely  separate  and  distinct  from  the  work  exterior 
to  it,  whatever  may  be  the  material  used  in  its  con- 
sti'uction.  In  a  field  work,  the  keep  is  built  of 
timber,  and  is  called  a  block-house. 

The  conditions  which  should  be  fulfilled  by  a 
block-house  intended  for  a  keep,  are  that  it  shall 
have  a  good  command  over  all  of  the  interior  space 
enclosed  by  the  outer  work,  and  shall  occupy  a  po- 
sition such  that  all  parts  of  the  exterior  work  can  be 
seen  from  it. 

The  plan  of  a  block-house  is  selected  by  the  same 
general  rules  which  are  used  for  selecting  the  trace 
of  a  field  work.  It  may  be  square,  rectangular,  oc- 
tagonal, and  even  cruciform,  in  plan,  according  to  the 
locality  in  which  it  is  placed  and  the  fire  which  it 
has   to   deliver. 


lo8  FIELD   FORTIFICATIONS. 

The  dimensions  of  a  block-house  should  be  suflBc- 
ient  to  allow  sleeping  accommodations  for  the  men  who 
are  to  occupy  it;  and  in  some  cases  allowance  should 
be  made  for  other  accommodations.  Its  interior  dimen- 
sions should  give  at  least  a  height  of  six  feet  in  the 
clear  for  the  rooms  ;  a  height  of  eight  or  nine  feet 
gives  better  accommodations  and  better  ventilation. 

The  width  of  the  interior  should  not  be  less  than 
nine  feet  in  the  clear,  as  this  is  the  least  distance 
which  can  be  used  and  give  room  for  a  passageway 
and  a  row  of  bunks. 

The  length  of  a  block-house  will  depend  upon 
the  number  of  men  it  has  to  accommodate,  after  the 
width  has  been  assumed. 

Block-houses  must  be  made  strong  enough  to  re- 
sist the  projectiles  which  may  strike  them  and  should 
be  proof  against  fire  and  splinters. 

They  should  be  free  from  dampness,  and  should 
be  well  ventilated. 

The  conditions  given  for  a  bomb-proof  are  ap- 
plicable to  the  block- house,  with  the  additional  one  of 
arranging  its  walls  for  defence. 

This  is  fulfilled  by  perforating  the  walls  with 
loop-holes  for  musketry  and  embrasures  for  cannon, 
when  the  latter  are  used. 

The  example  given  in  Figs.  53,  54,  and  55,  shows 
the  details  of  construction  of  a  wooden  block-house, 
used  in  the  late  war  in  the  United  States. 


INTERIOR   ARRANGEMENTS   OF  A   FIELD    WORK,    159 

The  walls  were  made  of  two  thicknesses  of  logs 
(Fig.  53)  the  inner  row  being  vertical,  the  outer  row 
being  horizontal. 


Fig.  53. 


Fig.  54. 


The  inner  row  was  composed  of  logs  in  contact, 
framed  into  a  ground-sill,  and  capped  by  a  heavy 
piece  of  timber.  The  logs  in  the  outer  row  were 
laid  one  upon  the  other,  having  a  surface  of  contact 
of  at  least  eight  inches. 

A  roof  of  logs  was  laid  upon  these  rows  forming 
the  walls,  and  then  boarded  over  to  make  it  water- 
tight. 


160  FIELD   FORTIFICATIONS, 

This  roof  was  covered  with  eanli  from  three  to 
four  feet  deep,  to  make  it  fire  and  splinter  proof. 

The  sides  exposed  to  the  enemy  were  banked  with 
earth  (Fig.  53)  to  increase  their  resistance  to  the 
enemy's  projectiles. 

Loop-holes  were  constructed  through  which  the 
defence  could  fire  upon  the  ground  exterior  to  the 
block-house. 

132.  Isolated  block  •  houses.  —  Timber  block- 
houses were  used  frequently  in  the  war  of  1861-5  in 
isolated  spots,  as  independent  works. 

In  these  places,  they  were,  as  a  rule,  exposed  to 
attack  only  from  infantry  or  cavalry,  or  a  few  pieces 
of  field  artillery. 

The  construction  shown  in  Figures  53.  54,  and  55 
is  a  type  of  these  isolated  block- houses. 

It  was  found  from  experience  that  it  required  a 
thickness  of  forty  inches  of  solid  timber  to  resist  the 
projectiles  of  field-guns. 

These  isolated  block-houses  were  frequently  built 
two  stories  high.  The  upper  story  was  usually  placed  so 
as  to  have  its  sides  make  an  angle  with  the  sides  of 
the  lower  story.  By  this  arrangement,  the  corners  of 
the  upper  story  projected  over  the  sides  of  the  lower. 
This  arrangement  of  the  upper  story  removed  the  dead 
space  near  the  sides  of  the  lower  story,  and  the  sector 
without  fire  in  front  of  the  angles.  Block-houses  ex- 
posed to  artillery  fire  should  not  have  a  second  story. 


INTERIOR   ARRANGEMENTS   OF  A   FIELD  WORK.     161 

133.  Stockades. — A  line  of  stout  posts  or 
trunks  of  trees  firmly  set  in  the  ground,  in  contact 
with  each  other,  and  arranged  for  defence,  is  called 
a  stockade. 

A  stockade  is  used  principally  when  there  is 
plenty  of  timber  and  little  or  no  danger  of  expos- 
ure to  artillery  fire.  It  is  frequently  used  to  close 
the  gorge  of  a  field  work,  and  to  guard  against  the 
work  being  carried  by  a  surprise,  by  bodies  of  in- 
fantry attacking  the  work  in  rear. 

The  timbers  of  a  stockade  may  be  either  round 
or  square.  If  round,  they  are  hewed  to  a  flat  surface 
on  two  of  the  sides  so  that  the  posts,  when  placed 
in  position,  shall  have  a  close  contact  of  at  least  four 
inches. 

The  top  of  a  stockade  should  be  at  least  eight  feet 


Fig.  56 


Fig.  57. 


above  the  ground  on  which  it  is  placed,  and  it  should 
have  the  upper  ends  of  the  timbers  sharpened,  or  ar- 
ranged with  spikes,  or  fixed  iu  some  way  to  offer  an 


1^)2  FIELD   FORTIFICATIONS. 

obstruction  to  climbing  over  the  top.  A  stockade  is 
arranged  for  defence  by  cutting  loopholes  (Figures  56, 
and  57,)  which  can  be  used  by  a  soldier  when  firing. 

The  height  of  the  loop-hole  may  be  just  four  feet, 
and  six  inches  above  the  ground,  or  higher. 

In  the  former  case,  the  soldier  stands  upon  the 
natural  surface  of  the  ground  (Fig.  56)  in  the  act  of 
firing  ;  in  the  latter  case,  he  stands  upon  a  banquette 
of  earth  (Fig.  57)  or  some  temporary  arrangement 
which  raises  him  to  tlie  proper  height. 

The  exterior  opening  of  the  loop-hole  should  be 
not  less  than  six  feet  above  the  ground  on  which  the 
enemy  may  stand  when  he  is  close  to  the  stockade,  so 
that  he  can  not  make  use  of  the  loop-hole.  Some 
obstruction  must  therefore  be  placed  in  front  of  the 

Fig.  58. 


loop-hole,  keeping  the  enemy  away  from  it ;  or  the 
ground  immediately  in  its  front  should  be  deepened 
by  digging  a  trench  (Fig.  56). 

If   the   loop-hole  can  be   placed  six  feet  above  the 


INTERIOR  ARRANGEMENTS   OF  A    FIELD  WORK.    163 

ground,  it  will  be  practicable  to  arrange  the  loop- 
holes so  as  to  furnish  a  double  tier  of  fire  (Fig.  58). 

The  loop-holes  of  the  lower  row  should  be  arranged 
so  that  they  can  not  be  used  by  the  enemy.  They 
should  not  be  higher  than  eighteen  inches  above  the 
ground  on  the  outside  ;  on  the  inside,  the  ground  must 
be  cut  away  (Fig.  58)  or  a  trench  dug  in  rear  of  the 
stockade,  so  as  to  allow  the  use  of  the  loop-holes  by 
the  defence. 

The  construction  of  a  loop-hole  in  a  stockade  can 
be  understood  by  examining  Fig.  59. 


Fig.  69. 


The  exterior  opening  of  a  loop-hole  is  represented 
by  a;  the  interior  opening  by  h,  A  side  view  is  rep- 
resented by  the  longitudinal  section  c. 

The  same  rules  govern  the  construction  of  loop- 
holes when  there  is  time  to  execute  them,  as  are  used 
in  constructing  embrasures  in  a  parapet. 

The  exterior  opening  is  made  as  small  as  possible 
and  serve  its  purpose.  An  opening  of  two  inches 
wide  and  five  inches  long  is  considered  sufficiently 
large  for  the  rifled  musket  of  the  present  day  (Art. 
108). 


164 


FIELD  FORTIFICATIONS, 


The  size  of  the  interior  opening  will  depend  upon 
the  field  of  fire.  A  width  of  six  inches  and  a  height 
of  twelve  inches  are  the  dimensions  usually  given  to 
the  interior  opening,  when  the  timbers  of  the  stock- 
ade are  twelve  inches  thick. 

When  there  is  a  great  hurry,  a  notch  may  be  cut 
by  an  axe  or  a  saw  in  each  of  the  logs,  which  will  do 
for  a  loop-hole.  The  front  of  this  notch  is  shown  by 
the  figure  d,  and  the  side  view  by  the  figure  /. 

A  perpendicular  cut  of  four  and  a  half  inches  is 
made  in  each  log  at  the  point  which  is  to  be  the  bot- 
tom of  the  loop-hole.  An  oblique  cut  is  then  made 
about  nine  inches  long.  The  two  logs  placed  in  con- 
tact form  a  loop-hole  as  seen  in  d  (Fig.  59). 

The  exterior  opening  may  be  reduced  afterwards 
by  spiking  a  piece  of  iron  upon  the  logs.      Kailroad 


Fig.  60. 


irif^ii  iT  1 


chairs,    fish-plates,   etc.,    frequently  found  in   the  vi- 
cinity, can  be  used  for  this  purpose. 

Sometimes  the  stockade  is  strengthened  by  a  second 
row  of  timbers.     The  method  is  shown  in  Fig  60. 


JNTERJOB   ARRANGEMENTS    OF  A   FIELD  WORK.     165 

This  figure  shows  also  the  method  of  making  loop- 
holes, by  cutting  away  a  strip  from  two  adjacent  posts, 
leaving  an  interval  through  which  the   men   can  fire. 

Loop-holes  are  usually  made  about  two  feet  and 
six  inches  apart 


CHAPTEE    XII. 

ARRAiq^GEMENTS    EXTERIOR    TO    THE    PARAPET. 

134.  Kinds. — There  are  two  kinds  of  arrange- 
meuts  employed  on  the  exterior  of  a  parapet  to  add 
to  the  strength  of  a  work^  viz  :  the  arrangements  made 
to  defend  the  ditch,  and  those  made  to  obstruct  an 
enemy's  approach. 

The  term,  ditch  defence,  is  used  to  designate 
the  arrangement  made  exterior  to  the  parapet,  by 
which  a  fire  is  made  to  sweep  the  ditch. 

The  term,  obstacle,  is  applied  to  any  construc- 
tion or  arrangement,  whatever  may  be  its  nature, 
which,  by  its  passive  resistance,  obstructs  the  ap- 
proach of  an  enemy  advancing  to  assault  the  work. 
Hence,  anything  is  an  obstacle  which  diverts  the  at- 
tention of  the  enemy  from  the  assault  to  the  imme- 
diate surroundings  of  himself. 

I.    Ditch  defences. 

135.  Classes  of  ditch  defences. — The  ditch 
is  best  defended,  as  a  general  rule,  by  the  work  itself. 
But  as  a  flanking  disposition  is  not  always  attainable, 
and  as  it  is  not  usually  practicable  in  field  works,  some 
arrangement  must  be  provided  by  means  of  which  the 


ARRANGEMENTS  EXTERIOR    TO    THE  PARAFE,T,    167 


ditches  can  be  swept,  in  those  works  where  it  is  neces- 
sary  that  the  dead  spaces  should  be  removed. 

The  constructions  used  for  this  purpose  are  either 
caponnidres  or  galleries. 

136.  Caponni^res. — A  caponniere  is  a  bomb- 
proof construction  built  in  the  ditch  (Fig  61). 

Fig.  61. 


B 


Superior  Slope 


It  may  be  arranged  for  a  fire  in  two  directions,  or 
only  in  one.     The  amount  of  fire  fixes  its  length. 

When  arranged  for  a  fire  in  two  directions,  it 
should  be  wide  enough  to  accommodate  two  ranks, 
facing  in  opposite  ways.  This  width  should  not  be 
less  than  eight  feet.  A  width  of  four  feet  and  six 
inches  is  sufficient  for  one  rank. 

The   interior  height  should   not  be   less   than    six 


HhS 


FIELD  FORTIFICATIONS, 


feet  in  the  clear  (Fig.  62).  The  bottom  of  the  capoa- 
ni^re  may  be  on  the  same  level,  as  the  ditch,  or  be- 
low it. 

Fig.  62. 


The  loop-holes  are  arranged  as  described  in  art. 
132.  The  top  should  not  rise  above  the  crest  of 
the  counterscarp  and  should  be  made  bomb-proof. 

Entrance  is  obtained  by  a  covered  passage,  P, 
leading  under  the  parapet.  It  is  constructed  by  using 
frames  like  those  described  in  Art.  117. 

The  construction  of  the  roof  and  the  position  of 
the  loop-holes  are  shown  in  Fig.  62,  which  represents 
a  cross  section  made  by  the  plane  A  Ba  in  Fig  61. 

137.  Galleries. — Galleries  used  to  sweep  the 
ditch  with  their  fires  are  constructions  similar  to  ca- 
ponnieres.  They  receive  the  name  of  scarp  or 
counterscarp  galleries,  according  to  the  position 
which  they  occupy. 

The  usual  method  of  building  a  gallery  is  to  ex- 
cavate the   earth   behind    the  scarp   or  counterscarp. 


ARRANGEMENTS  EXTERIOR    TO   THE  PARAPET,    169 

as  the  case  may  be,  until  there  is  room  to  place  the 
frame,  if  there  is  one  to  be  used,  or  until  there  is 
room  to  accommodate  the  men  who  are  to  occupy 
the  gallery.  This  excavation  is  then  closed  in 'front 
by  a  stockade  built  along  the  line  of  the  scarp  or 
counterscarp  ;  it  is  closed  overhead  by  a  bomb-proof 
roof,  the  top  of  which  is  the  parapet,  in  the  case  of 
a  scarp  gallery,  and  the  glacis  or  natural  surface  of 
the  ground,  if  a  counterscarp  gallery. 

The  arrangements  of  loop-holes,  dimensions,  etc., 
are  all  similar  in  kind  and  character  to  those  men- 
tioned for  caponnieres. 

Entrance  to  a  scarp  gallery  is  by  a  covered  pas- 
sage ;  the  same  might  be  used  for  a  counterscarp 
gallery ;  generally,  the  entrance  to  the  latter  is  by 
openings  into  the  ditch,  at  the  ends  of  the  gallery, 
which  openings  can  be  closed  by  bullet-proof  doors. 
Counterscarp  galleries  are  used  at  the  salients  of  a 
work ;  scarp  galleries  at  the  re-entrants. 

Scarp  and  counterscarp  galleries,  as  well  as  capon- 
nieres, are,  in  their  details  of  construction,  nothing  but 
stockades.  It  follows  then  that  all  remarks  relating 
to  stockades  apply  equally  to  these   ditch  defences. 

They  should  not  be  placed  in  positions  where 
they  would  be  exposed  to  artillery  fire.  If  there 
was  danger  of  exposure  to  this  fire,  and  it  was  ne- 
cessary to  use  of  one  these  defences,  it  is  plain  that 
the  counterscarp  gallery  is  to  be  preferred. 


170  FIELD   FORTIFICATIONS. 

It  may  be  remarked,  however,  that  ditch  defences 
of  this  kind  rarely  repay,  by  their  advantages,  the 
amount  of  time  and  labor  expended  in  their  con- 
struction; and  then,  only  in  the  case  of  a  large  en- 
closed work  with  deep  ditches. 

II.  Obstacles. 

138.  Kinds. — Obstacles  are  of  two  general  kinds, 
viz  :  natural,  and  artificial. 

Marshes,  water  courses,  precipices,  etc.,  are  exam- 
ples of  obstacles  of  the  first  kind.  A  very  little  labor, 
well  applied,  will  often  convert  these  natural  features 
of  the  ground  into  serious  obstacles  to  an  enemy's 
advance. 

Ditches,  abatis,  palisades,  slashings,  etc.,  are  ex- 
amples of  artificial  obstacles.  They  can  be  made 
important  adjuncts  of  a  defensive  work,  and  can  be 
made  to  perform  effective  service  in  the  defence  of 
any  position. 

139.  Ditches. — The  ditches,  from  which  the 
earth  is  obtained  to  make  the  parapet,  can  be  made 
into  obstacles  to  an  enemy's  assault.  To  offer  an 
obstruction  difficult  to  surmount,  a  ditch  should  be 
not  less  than  six  feet  deep  and  twelve  feet  wide. 
(Art.  28).  The  difficulties  of  surmounting  an  obstruc- 
tion of  this  kind  can  be  greatly  increased  by  making 
the   scarp  steep,   and  by  a  judicious  arrangement   of 


ARRANGEMENTS  EXTERIOR    TO    THE  PARAPET    171 


some  of  the  other  obstacles,  "  hereinafter  named,  in 
and  along  the  ditch. 

When  ttie  scarp  is  made  steep,  it  is  necessary 
to  revet  its  surface,  so  as  to  protect  it  from  the 
weather  and  to  hold  the  earth  in  place.  In  the 
late  war  in  the  United  States,  the  revetments  used 
for  the  scarps  of  works  when  strength  was  required, 
were  made  of  timber  or  plank. 

The  timber  scarp  revetment  (Fig.   63)  was  corn- 


Fig.  63. 


posed  of  logs  placed  in  contact  with  each  other, 
with  a  slight  slope,  about  V,  and  capped  by  a  log 
notched  on  the  uprights  ;  this  capping  log  being  tied 
back  to  an  anchor  log,  bedded  into  the  natural  soil 
and  held  in  place  by  pickets. 

The  plank  scarp  revetment  (Fig,  64)  differed  but 


172 


FIELD   FORTIFICATIONS. 


slightly  from  the  timber  revetment.  Tiie  posts,  in- 
stead of  being  in  contact  with  each  other,  were 
placed  from  six  to  eight  feet  apart,  and  the  earth  was 
held  up  by  planks  placed  on  edge  behind  the  posts. 

These  revetments  are  practically  the  same  as  the 
revetments  described  in  articles  81  and  82. 

The  timber  revetment  is  the  stronger  of  the  two, 
but  requires  more  time,  labor,  and  timber  to  construct 
it  than  the  plank  revetment. 

140.  Abatis. — A  row  of  large  limbs  and  branches 
of  trees,  with  the  ends  of  the  branches  sharpened, 
placed  with  the  points  towards  the  enemy,  forms 
the  obstacle  known  as  an  abatis. 

An  abatis  may  occupy  an  upright  position  in  a 
ditch   (Fig.  65)   or  it  may  lie  in  a  horizontal  position 


Fig.  65. 


on  the  ground   in   front   of   a  work    (Fig.   66).      The 
latter  is  the  usual  position  given  to  an  abatis. 

An  abatis,  to  be  an  efficient  obstacle,  should  con- 
sist of  stout  limbs,    twelve   or   15   feet  long,  laid   as 


ARRANGEMENTS  EXTERIOR    TO   THE  PARAPET.    1T3 

close  together  as  possible,  with  the  butts  secured  by 
stout  stakes,  and  should  not  be  exposed  to  the  enemy's 
artillery  fire.  When  laid  in  front  of  a  work,  it  is 
usual  to  protect  it  by  a  slight  glacis.     (Fig.  66.) 

Fig.  66. 


141.  Entanglement. — An  entanglement  made 
by  driving  stout  stakes  into  the  ground  from  six  to 
eight  feet  apart  and  connecting  them  by  stout  wire 
twisted  around  the  stakes,  forms  an  excellent  obstacle. 
(Fig.  67.)  It  is  quickly  made  when  the  materials  are 
close  at  hand. 


Fig.  67. 


142.  Che vaux-de-f rise, — A  cheval-de-frise  (Fig. 
68)  is  a  square  timber,  perforated  with  holes  in  which 
sticks  shod  with  iron  are  inserted.  The  holes  are 
placed  about  six  inches  apart,  and  are  large  enough 
to  admit  a  stick   of  at  least   two  inches   in  diameter. 


174 


FIELD   FORTIFWATIONS. 


These  sticks,  called  lanoes,  are  ten  feet  long,  and  are 
made  to  project  equally  on  the  two  sides  of  the  body, 
as  the  timber  is  called.     The  length  of   each  cheval- 

Pig.68. 


de-frise  is  from  six  to  ten  feet.  They  are  fastened 
together  at  the  ends  by  stout  wire,  or  by  chains. 

In  the  British  service,  portable  chevaux-de-frise 
made  of  iron,  and- in  lengths  of  six  feet,  are  used. 

143.    Palisades. — A  palisading  is  simply  a  fence, 

Fig.  69. 


made  of  strong  and  stout  poles  or  pickets   firmly  set 
into  the  ground  (Fig.  69). 

The  poles  are  placed  in  a  vertical    or  slightly  in- 


ARRANGEMENTS  EXTERIOR   TO   THE  PARAPET.    175^ 

clined  position,  with  intervals  between  them  of  about 
three  inches. 

The  poles  are  obtained  by  sawing  trunks  of  trees 
into  lengths  of  from  ten  to  twelve  feet,  and  splitting 
them  into  rails  of  not  less  than  four  inches  thick. 

The  palisade  is  formed  by  digging  a  trench  three 
feet  deep,  planting  the  rails  in  it,  and  ramming  the 
earth  around  them. 

The  rails  are  fastened  together  by  being  spiked  or 
nailed  to  a  stout  riband  piece  placed  about  a  foot 
below  the  surface  of  the  ground.  A  second  riband 
piece  is  used  about  a  foot  below  the  top  of  the  rails. 

It  is  usual  to  sharpen  the  rails  to  a  point  to  add  to 
the  difficulties  of  climbing  over  the  palisade. 


Fig.  70 


144.  Fraises. — A  palisading  occupying  a  hori- 
zontal position   (Fig.  70)   is  called  a  fraise. 

145.  Small  pickets. — Small  straight  branches 
of  hard  and  tough  wood  are  frequently  cut  into  short 


176  FIELD  FORTIFICATIONS. 

lengths,  driven  firmly  into  the  ground,  leaving  from 
one  to  two  feet  projecting,  and  pointed  at  the  upper 
end.  Obsti'uctions  of  this  kind  are  called  small 
pickets  (Fig.  70). 

146.  Crow's  feet,  harrows,  etc. — Obstacles  of 
other  kinds  having  the  same  object  in  view  as  small 
pickets  are  sometimes  used.  The  most  noted  are  the 
obstacles  known  as  crow's  feet ;  ordinary  harrows 
turned  upside  down  with  the  teeth  upwards  and  the 
frames  buried  ;  planks  with  spikes  driven  into  them, 
placed  so  as  to  have  the  points  upwards  ;  etc. 

A  crow's  foot  is  made  of  four  stout  iron  spikes, 
welded  together  at  their  heads,  and  arranged  so  that 
in  whatever  position  the  obstacle  is  thrown  upon  the 
ground,  one  of  its  points  shall  stand  upwards. 

.  147.  Military  pits. — Excavations  made  in  the 
ground,  conical  or  pyramidal  in  form,  with  a  small 
picket  driven  into  the  bottom,  are  called  military 
pits.  (French,   frous-de-loup.) 

They  are  of  two  kinds,  viz  :  deep  and  shallow. 

Deep  military  pits  (Fig.  71)  should  not  be  less 
than  six  feet  in  depth,  so  that  if  they  fall  into  the 
possession  of  the  enemy,  they  can  not  be  used  against 
the  defence. 

They  are  usually  made  about  six  feet  in  diameter  at 
top.  and  about  one  foot  at  the  bottom,  and  are  placed 
so  that  the  centres  shall  be  about  ten  feet  apart.  They 
should  be  placed  in  rows,  at  least  three  in  number,  the 


ARRANGEMENTS  EXTERIOR    TO    THE  PARAPET,    17? 

pits  being  in  quincunx  order.  The  earth  obtained  by 
the  excavation,  should  be  spread  over  the  ground  be- 
tween the  pits. 


Fig.  71. 


Shallow  pits  should  not  be  deeper  than  about 
two  feet,  so  tliat  the  enemy  could  not  obtain  shelter 
by  getting  into  them. 

They  should  cover  the  ground  in  a  zig-zag  -ar- 
^angement,  the  upper  bases  being  made  square  or 
.ectangular  in  form,  and  in  contact  with  each  other. 
The  side  of  the  upper  base  should  be  made  about 
equal  to  the  depth  of  the  pit.  The  earth  obtained 
from  the  holes  is  thrown  in  front  of  the  arrangement, 
making  a  ghicis. 

148,  Slashing. — In  compliance  with  the  princi- 
ple that  all  houses,  trees,  brushwood,  etc.,  should 
be  removed  within  range  of  the  work,  which  could  be 
used  as  a    shelter  and  a  place  of  concealment  by  the 


178  FIELD  FORTIFICATIONS, 

enemy's  sharp-shooters,  it  is  essential  that  the  trees 
within  six  hundred  yards  of  the  work  should  be  cut 
down. 

As  it  is  not  practicable  to  remove  immediately 
the  trees  from  the  spot,  it  is  the  custom  to  cut  them 
down  so  that  they  shall  form,  while  lying  on  the 
ground,  an  obstacle  which  may  be  used  in  the  de- 
fence of  the  work. 

Trees  cut  down  so  as  to  fall  in  all  directions, 
form  what  is  known  as  a  slashing.  It  is  better, 
where  the  trees  are  intended  to  be  used  as  an  obsta- 
cle, that  they  be  cut  so  as  to  fall  towards  the  enemy  ; 
and,  in  the  case  of  the  smaller  trees,  which  might  be 
moved  by  a  few  men,  the  trunks  should  not  be  cut 
entirely  through,  but  only  enough  to  allow  the  trees 
to  fall.     (Fig.  72.) 


Fig.  72 


A  thick  and  well  arranged  slashing  forms  an  ex- 
cellent obstruction  to  an  enemy's  free  movements.  It 
has  the  serious  defect  of  being  easily  burned  when  dry. 

149.  Torpedoes. — Loaded  shells  buried  in  the 
earth    just    deep   enough    to     be    concealed,    and   ar- 


ARRANGE3IENTS  EXTERIOR    TO    THE  PARAPET.    179 

ranged  so  that  they  can  be  exploded  automatically,  or 
at  the  will  of  the  defence,  have  been  nsed  as  obstacles. 
Arrangements  of  this  kind  are  known  as  torpedoes. 

The  case  enclosing  the  charge  may  be  either  of 
wood  or  iron.  Condemned  shells  are  especially  suita- 
ble for  the  purpose. 

The  explosive  compound  used  to  charge  them 
may  be  powder,  gun-cotton,  nitro-glycerine,  or  any 
material  which,  upon  being  fired,  will  burst  the  case 
containing  the  charge  and  scatter  the  fragments  in 
every   direction. 

The  automatic — sometimes  known  as  the  ''  sensi- 
tive "  torpedo — is  fired  by  contact.  It  has  the  advan- 
tage of  being  exploded  at'  the  right  time,  but  has  the 
disadvantages  of  making  the  ground,  in  which  it  is 
buried,  dangerous  to  the  defence,  and  of  subjecting 
the  men  when  handling  it  to  the  danger  of  acciden- 
tal explosions. 

The  torpedo  which  is  fired  '^at  will"  has  the  dis- 
advantage of  being  fired  oftentimes  prematurely,  or 
when  it  is  too  late. 

Circumstances  can  only  decide  as  to  which  of  the 
two  is  to  be  preferred  as  an  obstacle. 

150.  Stone-fougasses. — Military  mining  is 
rarely  resorted  to  either  in  the  attack  or  the  defence 
of  a  field  work.  When  used,  it  forms  part  of  the 
operations  of  a  siege,  which  may  sometimes  be  under- 
taken to  get  possession  of  a  field  work. 


180  FIELD   FORTIFICATIONS. 

A  mine  placed  at  the  bottom  of  a  small  shaft  and 
fired  by  a  fuze,  is  termed  a  fougasse. 

A  particular  arrangement  known  as  the  stone- 
fougasse  is  always  described  by  military  writers  on 
the  subject  of  field  works  as  a  useful  device  in  the 
defence  of  a  work. 

It  is  usually  constructed  by  excavating  a  funnel 
shaped  hole  in  the  ground  to  a  depth  of  five  or  six 
feet.  The  axis  of  the  excavation  has  an  inclination 
of  about  40°  with  the  horizon  ;  the  lower  line  has  an 
inclination  of  about  30°. 

A  box,  containing  the  powder,  is  placed  in  the  bot- 
tom of  the  hole,  and  covered  by  a  wooden  shield  which 
exactly  fits  the  excavation.  The  earth  of  the  excava- 
tion is  well  rammed  around  the  shield  on  top  and 
behind,  so  as  to  make  the  line  of  least  resistance 
offered  to  the  explosion  coincide  as  nearly  as  possible 
with  the  axis  of  the  excavation.  On  this  shield  and 
in  this  hole  are  poured  from  three  to  five  cubic  yards 
of  stones,  the  smallest  weighing  one  pound.  Some- 
times loaded  shells  are  mingled  with  the  stones. 

The  fougasse  is  fired  by  means  of  a  fuze,  or  by 
electricity,  in  a  similar  manner  to  that  used  for  firing 
mines. 

The  result  of  the  explosion  is  to  scatter  the  stones 
in  a  shower  over  a  considerable  extent  of  ground  in 
front  of  the  fougasse. 

The    whole  construction  is  simply  an  extemporized 


ARUANaKMENTS  EXTERIOll    TO    THE   PARAPET,     181 

mortar  for   throwing  stones,  capable   of  a   single   dis- 
charge. 

Its  position  must  be  concealed  from  the  enemy's 
view. 

151.  Shell-fougasses. — A  shell  fougasse  is  a 
box  containing  loaded  shells,  concealed  in  the  earth, 
and  so  arranged  as  to  be  exploded  when  the  enemy- 
is  over  the  spot. 

The  box  is  divided  by  a  partition  into  two  parts, 
an  upper  and  a  lower.  The  loaded  shells  are  placed 
in  the  upper  part,  with  the  fuzes  downwards  and  con- 
necting with  the  lower  part  by  holes  bored  in  the 
partition. 

A  charge  of  powder  is  placed  in  the  lower  division 
of  the  box  of  sufficient  quantity,  when  fired,  to  throw 
the  shells  to  the  surface.  This  charge  is  fired  by 
means  of  a  fuze,  or  by  electricity,  like  other  fougasses. 

152.  Inundations. — If  the  position  occupied  by 
a  field  work  is  near  a  stream,  it  may  be  possible,  in 
some  cases,  to  increase  the  difficulties  of  the  enemy's 
approach  by  inundating  the  ground  over  which  he 
has  to  pass.  The  inundation  may  be  produced  by 
building  dams  and  causing  the  waters  of  the  stream 
to  overflow  its  banks. 

If  the  depth  of  the  water  over  the  approaches  is 
greater  than  five  feet,  the  obstacle  may  be  considered 
as  practically  insurmountable. 

If  the  depth  is  less,   the  obstacle  is  still  a  serious 


IS2  FIELD   FORTIFICATIONS. 

one,  and  can  be  made  greater  by  digging  pits  and 
ditches  at  random  and  having  them  covered  with  a 
sheet  of  water.  The  ditches  of  the  work,  ah-eady  im- 
portant obstacles  in  themselves,  can,  by  flooding  them, 
be  made  almost  impassable. 

153.  Uses  of  obstacles. — No  obstacle  is  in- 
surmountable. Obstacles  may  hinder,  and  even  stop 
for  a  while,  an  enemy ^s  approach,  but  they  can  be  over- 
come. Their  passive  resistance  must  be  aided  by  the 
active  resistance  of  the   defence. 

These  obstacles,  in  order  that  they  should  be  ac- 
cessory means  of  defence,  should  detain  the  enemy 
in  a  position  where  he  will  be  under  the  fire  of  the 
defenders  at  close  range.  Hence,  the  following  con- 
ditions should  be  observed  in  arranging  the  obstacles 
in  front  of  a  field  work. 

1.  The  obstacles  should  be  placed  within  close 
musketry  range  of  the  defence. 

2.  They  ^  should  be  arranged  so  as  not  to  afford 
shelter  to  the  enemy. 

3.  They  should,  as  a  rule,  be  protected  from  the 
fire  of  the  enemy's  artillery. 

4.  They  should  be  arranged  so  as  not  to  interfere 
with  an  active  defence  of  the  work. 

Their  uses  as  obstacles  will  depend  upon  the  de- 
gree of  resistance  which  they  offer  in  harmony  with 
the  foregoing  conditions. 

Abatis  placed  in  the  ditch  will,  in  one  case,  be  in 


ARRANGEMENTS   EXTERIOR    TO    THE   PARAPET.    183 

the  best  position ;  in  another,  it  should  be  placed  some 
distance  in  front  of  the  work. 

A  f raise  placed  in  the  scarp,  when  the  ditch  is 
swept  by  a  fire  from  the  work  or  from  ditch  de- 
fences, will  be  better  than  if  along  the  counterscarp. 

Torpedoes,  military  pits,  entanglements,  etc.,  may 
all  be  combined.  In  some  cases,  the  ground  in  front 
of  the  work  will  be  the  better  position  ;  in  others,  the 
crest  of  the  counterscarp  and  the  ditches  offer  the 
best  conditions  for  their  use. 

As  a  general  rule,  it  is  advisable  to  place  the  ob- 
stacles not  nearer  than  fifty  yards  to  the  interior 
crest,  if  the  profile  is  a  weak  one.  When  the  profile 
is  strong,  ic  is  not  a  matter  of  so  much  importance, 
so  long  as  the  assaulting  columns  are  exposed  to  the 
fire  of  the  defence. 

It  is  well  to  remark  with  respect  to  inundations, 
that  they  should  not  be  used  until  the  last  moment. 
The  unheal thiness  due  to  the  presence  of  stagnant 
water  is  apt  to  produce  more  casualties  than  are  to 
be  feared  from  the  enemy's  attacks. 

If  the  dams  can  not  be  protected  or  hidden  from 
the  enemy's  artillery  fire,  they  should  be  built,  as  far 
as  possible,  so  that  the  enemy  can  bring  his  fire  to 
bear  only  upon  the  upper  side.  The  amount  of  the 
dam  exposed  to  his  fire  will  then  only  be  the  portion 
between  the  top  and  the  surface  of  the  water. 


CHAPTER    XIII. 

FIELD   FORTIFICATIONS   UPON"   IRREGULAR    SITES. 

154.  General  considerations. — In  the  preced- 
ing chapters,  the  site  of  the  field  work  and  the 
ground  in  its  immediate  vicinity  were  considered  as 
practically  level. 

The  casQ  now  to  be  considered  is  the  one  in  which 
the  site  and  the  ground  in  the  immediate  vicinity  of 
tlie  work  are  irregular  in  formation. 

It  has  been  seen  how  the  trace  and  the  profile  of 
a  work  are  modified  by  the  presence  of  neighboring 
heights,  which  command  tlie  work.  (Chap.  X.)  It 
is  now  to  be  shown  how  the  irregularities  of  the 
site  modify  the  profile  and  trace  of  a  work. 

A  compliance  with  the  first  principle  given  for 
fortifications  (Art.  7)  w^ould  require  that  the  work  be 
placed  upon  the  high  ground,  rather  than  upon  the 
low  ;  a  compliance  with  the  second  principle  would 
require  that  the  parapets  be  placed  near  the  brow  of 
a  height  and  not  away  from  it.  Hence,  it  is  seen 
that  the  trace  of  a  work  generally  follows  the  brow 
of  the  high  ground  forming  its  site,  and  is  placed 
so  that  the  work  can  sweep  with  its  fires  the  slopes  in 
front  of  the  parapet. 


FIELD  FORTIFIC'ATIO.XS  UPON  IRRKGULAU  SITES.    185 

155.  Three  cases  will  arise.  The  case  in  which 
the  slopes  of  the  site  are  gentle,  easily  ascended, 
and  can  be  swept  by  front  and  direct  fires  of  artil- 
lery. The  case  in  which  the  slopes  can  be  ascended 
by  infantry  without  difficulty,  but  are  too  steep  to  be 
swept  by  a  direct  artillery  fire.  And  the  case  where 
the  slopes  are  so  steep  as  to  be  ascended  only  by 
climbing. 

The  first  case^  or  when  the  slopes  are  gentle,  is 
the  one  most  frequently  under  consideration. 

156.  Modification  of  profile. — Suppose  a  field 
work  to  occupy  a  surface  which  is  level  or  slightly 
undulating  considerably  above  the  surrounding  coun- 
try, but  joined  to  it  by  gentle  slopes.  It  will  be 
easily  seen  that  a  change  of  position  in  the  lines  of 
a  work  upon  this  plateau  can  only  be  made  by 
modifying  the  profile. 

Take  a  site  like  that  shown  in  Fig.  73,  and  sup- 
pose the  general  directions  in  ^which  a  strong  direct 
fire  must  be  had  (second  principle  of  trace.  Art.  36), 
to  be  indicated  by  the  lines  X  Y,  Xi  Yi?  'ind  Xs  Yst 
(Fig.  73).  The  lines  A  D,  A  B,  and  B  C,  drawn  per- 
pendicular to  the  lines  just  named,  would  indicate  the 
directions  that  the  interior  crests  should  have  to  get 
these  direct  fires. 

The  next  point  is  the  placing  of  these  lines  so 
that  the  fire  from  them  shall  sweep  the  slopes  in 
their  front. 


J  86 


FIELD   FORTIFICATIONS, 


Suppose  a  profile,  X'  Y'  (Fig.  74)  to  be  made 
representing  the  section  cut  out  by  the  plane  X  Y- 
(Fig.  73.) 

Fig.  73. 

Iy 


This  profile  gives  -the  inclination  of  the  slope  con- 


necting the  lower  level  with  the  high  ground.  An 
examination  of  the  profile  makes  it  plain  that  a  work 
placed  on   the  plateau,    B  H?  should   not  be   too  near 


FIELD  FORTIFICATIONS  UPON  IRREGULAR  SITES.    187 

B,  nor  too  far  away  from  it.  If  too  near,  the  guns 
can  not  be  depressed  enough  to  sweep  the  slope,  B  F* 
If  too  far,  the  brow,  B?  of  the  high  ground  will  in- 
tercept the  shots  and  make  a  dead  space  of  the  slope. 

If  a  straight  line,  p  B?  be  drawn  tangent  to  the 
slope,  or  so  that  no  point  of  it  should  be  more  than 
eighteen  inches  from  the  ground,  and  the  interior 
crest  of  the  work  be  placed  upon  it,  it  is  plain  that 
the  whole  slope  can  be  swept  by  a  direct  fire  of  the 
work,  so  long  as  the  angle  made  by  this  line  with 
the  horizontal  is  not  greater  than  that  made  by  the 
superior  slope  of   the  parapet. 

If  the  face,  A  B  (^^S-  "^3)  occupies  such  a  posi- 
tion that  the  interior  crest,  eight  feet  above  the 
ground  on  which  it  is  placed,  is  in  this  line,  F  P  (Fig. 
74),  then  it  is  evident  that  the  slope  can  be  thor- 
oughly swept  by  its  fire  if  the  inclination  of  the  slope 
is  not  greater  than  that  of  the  superior  slope. 

It  will  also  be  seen,  if  the  vertical  at  P  (Fig.  74) 
represents  this  position  of  the  interior  crest,  that 
moving  P  nearer  to  B  can  only  be  effected  by  lowering 
the  parapet  ;  or,  moving  it  away  towards  W,  by  rais- 
ing the  parapet ;  otherwise  the  slope  would  not  be 
swept  by  a  direct  fire  from  the  face  A  B- 

The  foregoing  sufficiently  explains  how  the  profile 
may  be  modified,  with  respect  to  the  height  of  the 
parapet  and  inclination  of  the  superior  *  slope,  for  the 
purpose  of  obtaining  a  direct  fire. 


188 


FIKL  J)    FO 1!  riFICA  TIOXS. 


167.  Modification  of  trace. — It  is  not  always 
practicable,  by  moving  the  parapet,  to  arrange  the 
trace  of  a  work  so  that  a  direct  fire  can  be  obtained 
upon  the  slopes  in  its  front.  This  is  particularly 
the  case  in  steep  slopes,  and  upon  ground  in  which 
the  contours  are  very  irregular  in  form.  Slopes  un- 
seen by  direct  fire  may  be  swept  sometimes  by  a 
flanking  fire  from  other  parts  of  the  work,  or  other 
works  built  for  the  purpose.  Circumstances  will 
decide  as  to  the  method  which  will  best  effect  the 
object. 

As  an  example,  take  the  case  of  a  piece  of  ground 
with  an  irregular  outline,  like  that  shown  in  Fig.  75. 


The   plan  *of  laying  out   the   trace  parallel  to  the 
brow   would  not   be  a  good   one,  because  of   the  great 


FIELD  FORTIFICATIONS  UPON  IRREGULAR  SITES,    189 

development  of  interior  crest  which  would  result,  and 
even  with  that,  a  failure  to  obtain  all  the  direct  fire 
needed. 

A  better  plan  would  be  to  modify  the  trace,  and  to 
make  use  of  a  line  with  intervals. 

A  line  of  works  like  Q,  A>  ^^c.,  might  be  placed 
upon  the  salient  spurs  and  in  defensive  relations  with 
each  other.  A  second  line,  as  R,  etc.,  might  be 
used  to  defend  the  ground  between  the  works  in  the 
first  line,  and  to  reach  points  not  seen  by  the  fire  from 
these  works. 

Or,  if  it  is  desirable  to  use  a  '^  continued  line,"  and 
it  is  not  expedient    nor  judicious   to  follow  the  brow 


Scale:  100  yds.to  1 


of  the  heiofhts.  a  trace  like  that  shown  m  Fig.  76 
may  be  used.  The  general  direction  in  which  the  fire 
of  the  enemy  is  to  be  expected  is  shown  by  the  arrow. 


J  90  FIELD   FORTIFICATIONS. 

The  trace,  instead  of  following  the  brow,  runs  from 
A  to  B  along  ground  considerably  lower  than  these 
points.  A  strong  work  should  be  built  upon  each  of 
the  points  A  and  B?  and  an  indented  line  receding,  as 
it  descends  the  slope,  should  join  these  works.  The  long 
branches  should  be  directed  so  as  to  be  safe  from  enfi- 
lading fire,  and  the  short  branches  arranged  to  bring 
flanking  fires  upon  the  slopes  in  front  of  the  faces. 

The  advantages  of  such  a  line  when  compared 
with  a  straight  line  joining  the  two  points,.  A  and  B? 
are  manifest. 

158.  Defence  of  steep  slopes. — The  brow  of 
the  height  where  the  slopes  are  too  steep  for  direct 
artillery  fire  may  be  broken,  forming  spurs  ;  or  the 
brow  may  be  regular  in  form. 

In  the  former  case,  works  are  placed  upon  the 
spurs,  and  the  slopes  in  front  of  the  works  are  swept 
by  fires  from  the  adjacent  works,  or  by  auxiliary  works 
constructed  for  the  purpose.  In  the  latter  case, 
the  works  should  be  arranged  to  bring  as  strong  an 
artillery  fire  as  practicable  upon  the  approaches  to  the 
foot  of  the  hill,  and  supplemental  flanking  arrange- 
ments should  be  used  to  sweep  the  slopes  with  mus- 
ketry fire. 

Under  circumstances  like  these,  the  works  are  not 
usually  exposed  to  a  close  artillery  fire,  and  they  are 
not  therefore  required  to  be  so  strong.  The  profiles 
may  be  modified  accordingly. 


^\  B  H  A  F?  y- 

OF  THK  > 

UNIVERSITY 
FIELD  FORTIFICATIONS  UFON^^^^^^^fUj^LR.^ 

159.  Defence  of  precipitous  slopes.— When 

the  slojDes  are  so  steep  as  to  be  ascended  only  by 
climbing  by  using  the  hands  in  the  ascent,  their 
defence  is  an  easy  matter. 

The  works  to  be  constructed,  unless  exposed  to 
cannon  fire,  may  have  a  very  slight  profile.  A  parapet 
four  feet  and  six  inch  inches  high,  and  thick  enough 
to  resist  musketry,  will  be,  as  a  rule,  all  that  is 
necessary. 

Ditches,  as  obstacles,  will  not  be  necessary.  A 
suflBcient  obstruction  can  be  obtained  by  scarping 
the  slope,  effected  by  cutting  away  its  face  until  a 
steep  slope  is  made.  If  a  ditch  is  used,  it  will  be 
placed  ordinarily  in  rear  of  the  parapet. 

If  the  high  ground  terminates  in  a  plateau  or 
large  flat  surface,  it  would  be  well  to  establish  a  line 
of  strong  field  works,  some  two  or  three  hundred 
yards  in  rear  of  the  brow,  which  would  command  the 
works  placed  along  the  crest  of  the  slope. 

160.  General  plan. — The  defence  of  a  position 
is  made  in  accordance  with  some  general  plan,  which 
plan  decides  as  to  the  predominance  of  the  offensive 
or  defensive  features  of  the  position,  the  points  to  be 
fortified,  the  number  of  troops  that  can  be  spared 
to  occupy  the  fortifications,  and  the  time  in  which 
the  works  must  be  built. 

After  these  general  points  are  fixed,  the  engineer 
may    then    consider    the   kind    of    works   which   will 


192  FIELD  FORTIFICATIONS, 

be  best  fitted  for  the  purposes  intended,  and  arrange 
the  profile,  defilade,  and  construction  according  to 
the  natural  features  of  the  site  and  the  means  at  his 
disposal  to  build  the  works.  The  position  should  be 
well  selected,  since  no  amount  of  skill  can  remedy  de- 
fects which  are  fatal.  The  faults  may  be  ameliorated, 
but  the  position  can  not  be  made  a  strong  one  if 
inherently  weak.  The  engineer  shows  his  skill  in 
adapting  his  constructions  to  those  positions  which 
in  themselves  have  some  merit.  This  adaptation  re- 
quires a  thorough  knowledge  of  the  principles  of  for- 
tification and  of  the  details  of  the  art. 

How  extensive  these  modifications  may  be  can 
be  seen  by  the  examples  just  given. 

Bridge-heads. 

161.    Definition,  —  The    term,     bridge-head, 

(French,  tete-de-ponf)  is  applied  to  any  field  work  or 
line  of  works  which  is  built  to  defend  a  crossing  of 
a  river  at  a  particular  point,  and  to  prevent  its  use 
by  an  enemy. 

These  crossings  are  made  by  means  of  bridges, 
ferries,  or  fords.  Of  these,  the  bridges  are  the  most  re- 
liable for  all  stages  of  water,  are  the  most  convenient, 
and  are  the  constructions  which  are  usually  guarded 
and  defended  with  the  greatest  care.  The  principles 
governing  their  defence  are  equally  applicable  to  the 
defence  of  fords  or  ferries. 


FIELD  FORTIFICATIONS  UPON  IRREGULAR  SITES.    193 


162.  Object. — The  object  to  be  attained  by  the 
use  of  a  bridge-head  is  to  protect  the  bridge  from 
the  destructive  measures  of  an  enemy,  and  to  prevent 
its  use  by  him. 

This  preservation  of  the  bridge  may  be  for  the 
purpose  of  keeping  open  the  communication  with 
the  opposite  bank,  with  the  expectation  of  using  it 
either  by  small   parties  or  by  large  bodies   of  troops. 

When  intended  for  the  use  only  of  small  bodies 
of  troops,  and  to  keep  possession  of  the  line  of  com- 
munication, the  bridge-head  used  for  the  defence  of 
the  bridge,  may  be  a  simple  field  work,  generally  a 
redan,  or  a  lunette.  (Fig.  77.) 
Fig.  77. 


This  half-closed  work,  a  redan  or  a  lunette,  L?  is 
usually  placed  on  the  road  leading  to  the  bridge  and 
upon  the  side  of  the  river  towards  the  enemy. 


194.  FIELD   FORTIFICATIONS. 

Its  rear  should  be  closed  by  a  stockade,  and  this 
stockade  connected  with  the  approaches  to  the  bridge, 
or  banks  of  the  stream,  by  a  palisade.  A  temporary 
road,  as  shown  by  the  dotted  lines,  should  be  built 
to  allow  of  a  free  passage  around  the  bridge-head,  in- 
stead of  going  through  it.  If  there  is  no  danger  of 
the  enemy  appearing  in  force  and  with  artillery,  a 
block-house  may  be  built  within  the  bridge-head. 

The  faces  and  flanks  of  the  bridge-head  should  be 
placed  so  as  to  intercept  all  fire,  that  the  enemy  can 
bring  upon  the  bridge  from  any  position  which  he 
might  occupy. 

If  there  is  danger  of  the  enemy  coming  in  force, 
either  to  destroy  the  bridge  or  to  cross  the  river  at 
this  point,  the  bridge-head  should  be  made  strong 
enough  to  resist  an  artillery  fire,  and  should  be 
strengthened  by  batteries  placed  in  positions  like  B?  B? 
B,  by  means  of  which  a  concentrated  fire  can  be  had 
upon  the  ground  in  front  of  the  bridge-head,  and  a 
fire  into  the  interior  of  the  work,  as  indicated  upon 
the  figure. 

Bridge-heads  of  this  kind  should  be  made  strong 
enough  to  hold  the  enemy  in  check  until  re-enforce- 
ments could  arrive,  or  until  the  bridge  could  be  made 
useless  to  the  enemy. 

Bridge-heads  of  this  simple  kind  are  useful  to 
protect  bridges  which  are  or  might  be  useful  for  recon- 
noitering  parties  composed  of  small  numbers. 


FIELD  FORTIFICATIONS  UPON  IRREGULAR  SITES.    195 

163.  Strong  bridge-heads. — A  bridge-head 
used  to  guard  a  crossing  when  the  army  may  move 
in  force,  either  to  make  an  advance  movement,  or  to 
retreat,  must  be  made  strong,  if  the  enemy  is,  or  is 
expected  to  be,  within  its  immediate  neighborhood. 

The  presence  of  bridges  already  constructed  may 
determine  the  selection  of  the  point  at  which  a  gen- 
eral may  desire  to  cross  his  army,  either  in  making  an 
advance  towards  the  enemy,  or  retreating  from  him. 

If  he  has  to  have  bridges  built,  he  will  have  some 
latitude  in  the  selection  of  the  point  at  which  he  may 
cross. 

The  selection  of  this  point  will  be  governed,  by 
strategical,    tactical,    and  technical  considerations. 

The  tactical  requirements  will  be  best  satisfied, 
as  a  rule,  when  the  point  of  crossing  lies  in  a  beud, 
with  its  convexity  towards  the  army  which  is  to  cross. 

The  bend  will  in  many  cases  allow  the  establish- 
ment of  batteries  from  which  flanking  and  cross  fires 
can  be  had  upon  the  ground  in  front  of  the  bridge- 
head (Fig.  77). 

The  banks  in  a  bend  are  usually  unequal  in  height, 
the  higher  bank  being  on  the  convex  side  and  op- 
posite to  the  bridge-head.  This  difference  of  height 
will  frequently  allow  the  site  of  the  bridge-head  to  be 
commanded  by  the  fire  from  the  opposite  bank. 

There  are  other  prominent  tactical  advantages  ac- 
companying  a   bend,    such   as   the   approaches    to   the 


190 


FIELD   FORTIFICATIONS. 


river  on  the  convex  bank  being  concealed  from  view 
of  those  on  the  opposite  side  ;  a  greater  protection 
being  obtained  for  the  bridge  structure  ;  etc. 

Great  as  these  advantages  are,  a  good  crossing  re- 
quires in  addition,  if  it  is  to  be  used  by  troops  mov- 
ing in  force,  a  roomy  space  in  front  of  the  bridge-head 
hidden  from  the  view  and  sheltered  from  the  fire  of  the 
enemy  in  which  the  masses  can  easily  deploy.  (Fig.  78.) 


In  this  ex;impl*\,  the  slielter  is  given  by  a  line  with 
nterv.-ils.  L-  L-  L-  l>ljiced  some  distance  in  front  of  the 


FTPJLD  FONTIFICATIOXS  UPON  IRREGULAR  SITES.    197 

bridge-head  and  encircling  the  space  to  be  occupied  by 
the  troops  in  their  movements  forward  from  this  point, 
or  in  retreat.  The  line  should  be  constructed  in  ac- 
cordance with  the  principles  already  laid  down  ;  the 
works,  in  defensive  relative  with  each  other,  and, 
where  necessary  supplemented  by  secondary  works. 

The  extremities  of  the  line  should,  as  in  this  case, 
rest  upon  the  river  or  upon  points  which  prevent  its 
being  turned. 

A  bend  in  the  river  enclosing  a  narrow  strip  of 
land  would  be  exactly  fitted  for  a  bridge,  and  for 
its  bridge-head,  but  would  not  be  so  favorable  for 
the  passage  of  large  bodies  of  troops,  because  of  tlie 
limited  space  afforded  to  the  masses  for  deployment 
after  having  crossed  the  river. 

There    is    shoAvn    only  one   bridge   in   the    figure. 
In   case  of  a   rapid   advance   being   made,  or   a   quick 
retreat  closely  followed  by  the  enemy,  several  bridges 
-  should  be  used. 

164.  Horn  works,  etc. — The  traces  used  for 
bridge-heads  are  of  various  kinds,  and  are  modified 
by  the  irregularities  of  the  site,  by  the  directions  of 
the  approaches,  and  by  the  forms  of  the  banks.  Ke- 
dans,  lunettes,  bastioned  lines,  cremaillere  lines,  etc,  of 
various  shapes  and  forms,  are  used. 

Certain  arrangements  of  the  bastioned  lines  give 
rise  to  the  bridge- heads  known  as  horn  works,  and 
crown  works. 


li>8  FIELD   FORTIFICATIONS. 

Let  a  poinfc  be  taken  in  front  of  the  bridge  and 
some  distance  from  it.  Through  this  point  let  a  right 
line  be  drawn  perpendicular  to  the  general  direction 
of  the  bridge.  On  this  line  thus  drawn  as  an  exterior 
side,  let  a  bastioned  front  be  constructed,  and  its  sali- 
ents be  joined  with  the  banks  of  the  river  by  straight 
lines,  which  are  so  directed  that  they  can  be  swept  by 
a  fire  from  the  opposite  bank.  The  resulting  trace  is 
known  as  a  liorn-work. 

It  is  plain  that  this  work  will  only  be  used  when 
the  main  approach  to  the  bridge  is  in  the  prolongation 
of  its  length. 

If  through  a  point  assumed  in  front  of  the  bridge 
two  right  lines  were  drawn  making  an  angle  with  each 
other,  and  prolonged  until  they  reached  the  banks  of 
the  river,  and  on  these  two  lines,  as  exterior  sides, 
bastioned  fronts  were  constructed,  the  resulting  trace 
would  be  that  of  a  crown-work. 

It  is  plain  that  this  trace  will  be  employed  when 
the  approaches  to  the  bridge  are  oblique  to  the  di- 
rection of  the  bridge,  and  that  the  enemy  would  use 
one  as  quickly  as  the  other. 

If  there  are  several  approaches,  and  the  entire 
front  is  exposed  to  attack,  a  continued  bastioned 
line  might  be  used,  enclosing  the  space  in  front  of 
the  bridge  from  bank  to  bank.  In  this  case,  if  a 
salient  occupies  the  central  position,  the  line  is  known 
as    a  crown-work.      In   the   latter  case  it  is  called   a 


FIELD  FORTIFICATIONS  UPON  IRREGULAR  SITES,    199 

complex  crown-work,  to  distinguish  it  from  one  con- 
structed on  two  sides  only,  which  is  called  a  simple 
crown-work. 

When  the  bridge  crosses  the  river  at  a  point 
where  there  is  no  bend,  it  is  frequently  the  case  that 
works  are  constructed  at  both  extremities  of  the 
bridge.  When  this  is  the  case,  the  works  form  what 
is  known  as  a  double  bridge-head,  to  distinguish 
it  from  those  just  described,  which  are  termed  single 
bridge-heads. 


OHAPTEK     XIV. 

HASTY    INTRENCHMENTS. 

165.  Hasty  defences. — Hasty  defences  include 
ail  extemporized  shelters,  which  are  quickly  con- 
structed (in  a  few  hours  at  most)  from  materials  found 
upon  the  spot  where  the  shelter  is  needed. 

In  consequence  of  the  effectiveness  of  modern  fire- 
arms, a  body  of  troops  can  not  retain  a  close  forma- 
tion for  a  single  hour  even,  if  in  the  presence,  and 
exposed  to  the  fire  of  an  enemy  in  force.  The  men 
are  forced  to  seek  shelter,  by  lying  down  on  the 
ground,  or  by  crouching  behind  any  slight  inequality 
which  may  exist  in  the  surface,  or  behind  some  kind 
of  a  screen  which  they  may  be  able  to  construct.  The 
screen  may  be  two  or  three  logs  rolled  together  (Frontis- 
piece), a  heap  of  fence  rails,  a  slight  mound  of  earth, 
or  anything  whatever  its  nature  which  will  hide  the 
soldier  from  the  enemy's  view.  , 

166.  Shelter-trenches. — The  simplest  form  of 
shelter,  for  a  soldier  'in  open  country,  under  ordinary 
circumstances,  is  a  shallow  trench,  which  will  furnish 
from  the  excavation,  sufficient  earth  when  lieaped 
upon  the  side  towards  the  enemy,  to  screen  the  soldier 
in   the  trench   from  the  enemy's    view.      Trenches  of 


HASTY  IXTRENCHMENTS.  201 

this  kind  are  known  us  shelter-trenches,  but  are 
most  frequently  called  by  the  soldier,  rifle-pits.  Be- 
cause of  the  shortness  of  time  required  to  build  these 
defences,  they  are  known  under  the  general  name  of 
hasty  intrenchments. 

Hasty  intrenchments  were  much  used  by  both  of 
the  contending  armies  in  the  late  war  in  the  United 
States.  They  were  used  so  frequently,  and  found  so 
efficacious,  that  the  men  acquired  the  habit  of  in- 
trenching their  line  immediately  upon  halting  after  a 
day's  march,  if  the  enemy  was  near.  No  compulsion, 
no  orders,  even,  were  necessary  for  the  men  to  begin 
this  work  ;  the  main  difficulty  was  to  make  them  de- 
lay long  enough  to  allow  a  proper  trace  to  be  marked, 
by  which  they  might  be  guided  in  the  construction  of 
their  line.  Instances  are  known,  where  the  men,  not 
having  intrenching  tools,  executed  the  trench  with 
the  bayonet  and  tin  cup.  These  shelter-trenches, 
thus  rudely  constructed,  were  deepened  and  strength- 
ened until  they  were  able  to  resist  field  artillery,  if  the 
position  was  to  be  occupied  for  any  length  of  time. 

Slight  as  these  defences  were  during  the  early 
stages  of  their  construction,  they  formed,  when  de- 
fended by  good  troops,  an  obstacle  difficult  to  over- 
come ;  and  they  were  captured  only  by  extraordinary 
effort,  accompanied  by  a  great  loss  of  life  on  the  part 
of  the  attacking  forces. 

167.    Construction. — The  trench  represented  in 


202  FIELD  FORTIFICATIONS, 

Fig.  79  is  the  smallest  that  can  be  made,  upon  level 
ground,  and  afford  shelter  to  a  man. 

Its  depth  in  rear  is  one  foot ;  its  width  is  five  feet ; 
and  its  length  is  dependent  upon  the  number  of  men 
using  it.  The  earth  taken  from  the  trench  and  heaped 
upon  the  ground  in  front  will  make  a  mound  fifteen 
inches  high  and  at  least  two  feet  thick,  affording  a 
screen  from  the  enemy's  view,  and  a  tolerable  shelter 
against  musketry  fire. 

A  log  laid  in  front  of  the  trench  and  the  earth 
thrown  over  and  against  it,  adds  materially  to  the 
protection  afforded  by  the  shelter. 

A  trench  of  this  kind  can  be  executed  by  the  soldier 
with  a  shovel  in  thirty  minutes. 

168.  In  one  hour's  time,  a  soldier  can  deepen 
and  strengthen  this  trench,  giving  to  it  a  depth  of 
eighteen  inches  throughout  its  width  of  five  feet,  and 
raising  the  mound  to  a  height  of  eighteen  inches.  (Fig. 
80).  This  additional  depth  of  trench  and  height  of 
mound  allow  the  soldier  using  it,  to  take  a  kneeling 
position  when  firing ;  a  position  more  convenient  than 
the  reclining  one  necessary  in  the  last  case. 

169.  In  from  two  to  three  hours'  time,  if  the 
soil  is  not  difficult  to  dig,  the  trench  can  be  enlarged 
to  a  width  of  eight  feet,  and  the  earth  excavated 
thrown  upon  the  mound,  raising  it  to  a  height  of 
three  feet  with  a  thickness  of  about  four  feet.  (Fig. 
81).     A   trench  of  these  dimensions  allows  the  soldier 


HASTY  INTRENCHMENTS, 


203 


to  occupy  a  standing  position  when  firing  and  it  ap- 
proximates to  the  form  of  trench  to  be  constructed 
finally,  if  there  is  time  for  the  purpose,  and  the  posi- 
tion is  to  be  held. 


Fig.  79. 


I^l!l2!^////f/////f'/f///yy'' 


W^^^^^^^^^W^W^' 


170.  It  will  be  observed  that  the  first  trench 
offers  no  serious  obstruction  to  the  advance  either 
of  artillery  or  cavalry.  In  the  latter  forms,  the 
trenches  will  obstruct,  more  or  less,  forward  move- 
ments, if  the  trenches  form  a  continuous  line. 

At  short  distances,  intervals  should  be  left  in  the 
line  of  the  trench,  or  ramps  be  arranged  in  the  trench, 
so  as  to  allow  the  artillery,  etc.,  to  march  straight 
over  the  intrenched  line  if  a  forward  movement  is  to 
be  made. 

171.  Covered      Communications.  — Shelter 


;>U4 


FIELD  FORTIFICATIONS, 


trenches  are  much  used  to  afford  covered  com- 
munications, along  a  given  front ;  to  connect  the 
works  in  a  •*  line  with  intervals ; "  to  bring  a  mus- 
ketry fire  upon  ground  which  can  not  be  swept  by  the 
fire  from  a  particular  work  ;  etc. 

The  least  dimensions  of  a  shelter  trench,  when 
used  as  a  communication  for  infantry  only,  are  given 
in  Fig.  82. 


Fig.  82. 


The  trench  should  be  made  three  deep,  and  four 
feet  wide  at  the  bottom.  The  earth  should  be  thrown 
on  the  side  towards  the  enemy,  and  then  levelled  off 
in  the  form  of  the  superior  slope  of  a  parapet,  so 
that  the  men  in  the  trench  can  fire  over  this  mass 
of  earth. 

If  the  trench  is  to  be  used  for  the  passage  of  ar- 
tillery, or  to  be  used  by  bodies  of  troops  passing  from 

Fig.  83. 


one  point   to  another  along  the  front,   its  dimensions 
should   be  those  shown  in  Fisr.  83. 


HASTY  INTRENCllMENTS.  205 

The  least  width  at  bottom  should  be  made 
eight  feet,  and  the  height  of  the  top  of  the  mound 
of  earth  should  be  at  least  six  feet  and  a  half  above 
the  bottom  of  the  trench.  The  side  of  the  trench 
toward  the  enemy  should  be  cut  into  off-sets,  and 
arranged  so  as  to  allow  a  fire  of  musketry  over  the 
parapet. 

172.  Trace  of  shelter  trenches.— Shelter 
trenches  are  rarely  made  to  follow  a  straight  line, 
but  usually  conform  to  the  contour  of  the  ground. 
The  trace  should  be  marked  on  the  ground  if  there 
is  time  to  do  it.  It  will  economize  the  labor  of  the 
troops,  and  avoid  an  unneccessary  waste  of  time. 

The  trace  should  be  governed  by  the  general 
rules  laid  down  for  field  works,  and  great  care  should 
be  taken  that  it  can  not  be  enfiladed  by  a  fire  of  the 
enemy. 

Profiles  are  not  necessary.  The  points  which 
would  be  occupied  by  them  may  be  marked  by 
men  standing  upon  the  edge  of  the  proposed  trench 
towards  the  enemy.  A  line  would  then  be  marked 
on  the  ground,  by  a  pick,  passing  through  the  points 
selected.  Parallel  to  this  line  and  twelve  or  fifteen 
feet  in  rear  of  it,  the  line  of  troops  should  be 
formed.  The  front  rank,  furnished  with  intrenching 
tools,  would  begin  the  digging  ;  the  rear  rank  would 
lie  down.  Reliefs  should  be  formed,  and  the  trench 
rapidly  executed. 


206 


FIELD  FORTIFICATIONS. 


173.  Shelters  for  artillery.— The  shelters 
for  artillery  or  cavalry  may  be  made  in  a  very  short 
time,  in  a  way  similar  to  that  shown  for  the  shelter 
trench  for  infantry. 

On  undulating  ground,  the  shelter  trench  for  in- 
fantry is  frequently  on  the  slope;  the  shelter  for  ar- 
tillery would  generally  be  on,  or  behind,  the  crest. 
(Figs.  84  and  85). 


Fig.  84. 


It  is  seen  that  a  piece  of  artillery  on  the  crest  of 
undulating  ground  can  be  quickly  run  under  cover, 
if  it  be  desirable.  (Fig.  84). 

This  cover  can  be  quickly  and  easily  improved, 
by  making  a  slight  excavation  and  arranging  a  mass 
of  earth  in  front  of  the  gun.  (Fig.  85). 


Fig^  85. 


Slopes  of  this  kind  could  be  used  for  infantry  as 
well  as  for  artillery  ;  and  where  a  simple  screen  is  the 
main  object  to  be  had,  the  communication  would  be 
along  the  reverse  slope. 


7  HASTY  INTRENCH3IENTS.  207 

174.  Defence  of  a  house. — It  frequently  hap- 
pens that  the  front  of  a  defensive  position  is  occu- 
pied by  one  or  more  houses.  The  houses  may  be  on 
the  line  of  battle,  or  they  may  be  close  to  it. 

If  they  can  be  readily  put  in  a  state  of  defence, 
they  are  so  arranged  ;  if  not,  they  should  be  torn  down. 

A.  house,  solidly  built  of  stone  or  brick,  and 
which  will  not  be  exposed  to  artillery  fire,  can  be 
readily  made  into  a  defence  of  considerable  strength. 
Brick  houses  with  slate  roofs  are  the  best  for  the 
purpose. 

The  first  thing  to  be  attended  to,  in  putting  a 
house  into  a  defensive  condition,  is  to  clear  the  space 
in  front  of  it  of  every  thing  which  would  screen 
an  enemy's  approach.  The  next  is  to  loop-hole  the 
walls,  making  at  least  two  tiers  of  fire  in  the  lower 
story.  The  loop-holes  in  the  upper  stories  should  be 
arranged  to  get  a  fire  as  close  as  possible  to  the 
foot  of  the  walls  of  the  building. 

Ditches  cut  near  the  walls,  and  the  earth  thrown 
against  them,  are  recommended  to  keep  the  enemy 
off  and  to  add  to  the  resistance  of  the  walls. 

All  doors,  sashes  of  windows,  etc.,  inflammable  in 
their  nature,  should  as  far  as  possible  be  removed  and 
the  openings  barricaded  by  sand-bags,  or  by  boxes 
and  barrels  filled  with  earth. 

Barrels  filled  with  water  should  be  placed  in  each 
room  to  put    out  any  fire   which  might  happen    to 


208 


FIELD   FORTIFICATIONS. 


break  out  in  them.  Earth  in  a  moist  state  might  be 
spread  upon  the  floors,  or  on  any  of  the  flat  surfaces, 
liable  to  take  fire,  to  prevent  their  burning. 

175.  Tambours. — A  house  which  has  projecting 
parts,  like  bay  windows,  can  be  readily  arranged  to 
give  a  cross  fire  in  front  of  its  salient  angles.  The 
same  result  may  be  obtained  where  two  houses  flank 
each  other.  Where  flank  defence  can  not  be  thus 
obtained,  it  may  be  had  by  using  constructions  known 
as  tambours.  ^Figs.  86  and  87.) 


Fig.  86 


A  tambour  is  a  stockade,  generally  redan-shaped 
in  plan,  placed  in  front  of  a  door  or  other  opening,  in 
the   wall    to  be  flanked,  and  arranged  with  loop-holes 


II A  STY  INTREXC  lUIENTS, 


200 


to  bring  a  tire  upon  the  ground  in  front  of  the  salients 
of  the  line  to  be  defended. 


Fig.  87. 


It  may  have  one  or  more  tiers  of  fire  ;  it  may  be  one 
story  high,  or  it  may  be  two. 

176.  Machiooulis  galleries. — Where  tambours 
can  not  be  employed,  a  flank  defence  may  be  obtained 
by  means  of  a  construction  known  as  the  machi- 
coulis gallery.  (Fig.  88).  The  object  of  this  con- 
struction is  to  bring  a  fire  upon  the  ground  along  the 
foot  of  a   wall. 

Where  balconies  exist,  galleries  of  this  kind  can  be 
made  from  them. 

If  no  balcony  belongs  to  the  house,  the  gallery  may 
be  formed  by  breaking  two  or  more  holes  through 
the  wall,  on  a  level  with  the  floor  of  the  second  story. 


210 


FIELD   FORTIFICATIONS, 


Through  the  holes  thus  made,  stout  beams  are  passed 
and  their  inner  ends  firmly  secured  to  the  joists  of  the 
floor.      These  beams  form   the   joists   of  the  gallery. 


Fig.  88. 


Fig.  89. 


and  they  may  be  braced,  or  not,  by  diagonal  pieces 
as  shown  in  Fig.  88.  On  the  outer  extremities  of  these 
joists,  a  musket-proof  shelter  is  constructed ;  this  shel- 
ter may  be  made  of  two  thicknesses  of  plank,  enclosing 
some  light  resisting  material. 

The  men  fire  through  the  bottom  of  the  gal- 
leries upon  the  ground  beneath,  using  pistols,  if 
they  have  them,  in  preference  to  the  musket  or  the 
rifle. 

177.  Expedients  similar  in  principle  to  the  machi- 
coulis gallery  are  used  to  bring  a  fire  upon  the  ground 
in  front  of  the  wall  of  a  house  where  the  gallery  can  not 
be  used.  One  of  these  is  shown  in  Fig.  89,  where  the 
sash  of    the  window    is   removed  and   a  musket  proof 


HASTY  IXTEENCiniEXTS.  211 

shelter  is  inserted  in  the  window  at  an  angle  so  as  to 
leave  an  opening  at  the  bottom  through  which  a  man 
can  fire  his  pistol. 

178.  Stone  walls,  hedges,  etc. — Obstructions 
like  stone  walls,  hedges,  etc,  can  be  utilized  in  the  de- 
fence of  a  position. 

High  stone  walls  can  be  loop-holed,  and  ar- 
ranged for  defence  in  a  way  similar  to  that  adopted 
in  stockades.  Low  stone  walls  may  have  shallow 
trenches  dug  behind  them,  and  the  earth  thrown 
over  and  against  the  wall.  The  top  of  the  wall 
can  then  be  crenelated  or  arranged,  with  improvised 
loop-holes. 

Hedges  can  be  made  into  serious  obstacles  to  au 
enemy's  progress,  and  can  be  quickly  converted,  by 
means  of  earth  thrown  against  them,  into  good  shel- 
ters, for  the  defence. 

179.  Woods. — If  the  woods  are  too  far  to  the 
front  to  allow  of  their  being  defended,  they  should  be 
cut  down,  or  *^  slashed,"  thus  forming  an  obstacle,  but 
not  a  screen  to  the  enemy. 

If  they  are  to  be  defended,  a  line  of  shelter  trenches 
may  be  constructed  along  the  outer  edge  of  the  woods, 
on  the  side  towards  the  enemy,  but  within  the  edge 
so  as  to  be  concealed  from  his  view.  A  thin  strip  of 
the  timber  may  be  cut  down  to  form  an  abatis  in 
front  of  the  intrenchments. 

Good  roads  and  open  spaces  should  be  arranged  in 


21)1 


FIELD   FORTIFICATIONS, 


HASTV  INTRENCHMENTS,  213 

the  woods  to  allow  the  troops  and  guns  to  move  about 
freely. 

180.  Roads. — The  roads  in  rear  of  a  position 
should  be  arranged  so  that  they  can  be  freely  used  by 
the  defence.  Those  in  front,  should  be  obstructed,  and 
in  every  way  made  useless  to  the  enemy.  Bridges  to 
be  used  by  the  defence  should  be  put  in  good  order  ; 
those  which  would  be  of  service  to  the  enemy,  should 
be  destroyed. 

181.  Intrenched  fields  of  battle. — All  hasty 
intrenchments  and  defences  have  their  primary  use  in 
defending  a  position  which  is  to  become,  in  a  short 
space  of  time,   the  scene  of  battle. 

The  principles  already  named,  as  necessary  to  be 
observed  in  fortifying  a  position  for  defence,  are  equally 
applicable  to  the  methods  used  to  intrench  a  line  on 
the  field  of  battle.  The  more  completely  the  general 
conditions  for  fortifications  are  fulfilled,  the  stronger 
will  be  the  intrenched  line. 

The  example  shown  in  Fig.  90  may  be  taken  as  an 
illustration  of  what  is  meant  by  an  intrenched  line  of 
battle. 

An  army  corps  is  supposed  to  be  marching  on  the 
road  from  A  to  B  (Fig.  90),  and  the  commander  is 
instructed,  if  the  enemy  appears  in  force,  to  take  a 
position  and  hold  him  in  check. 

The  position  selected  may  be  one  which  is  to  be 
held  only  for  a  short  period,  so  as  to  allow  time  for  the 


214:  FIELD  FORTIFICATIOSS. 

army  to  concentrate,  or  to  force  the  enemy  to  concen- 
trate his  forces  to  attack ;  or  it  may  be  one  in  which  a 
decisive  battle  is  to  be  fought. 

It  is  supposed  that  the  commander  of  the  army 
corps,  when  in  the  vicinity  of  A?  learns  of  the  approach 
towards  B  of  the  enemy  in  force,  and  he  feels  obliged 
to  hurriedly  occupy  a  position  to  resist  the  enemy's 
advance. 

A  reconnoissance  has  shown  him,  that  the  best 
natural  position  for  him  to  occupy  for  this  pur- 
pose, is  the  ground  between  L  and  R,  and  that  the 
distance  between  these  points  is  about  four  thousand 
yards. 

He  finds  that  the  high  ground  runs  nearly  perpen- 
dicular to  his  line  of  retreat  through  A-  '*^^^^  is  bounded 
upon  the  right  by  an  unfordable  stream  with  low  and 
marshy  banks.  He  finds  the  ground  higher  where  the 
main  road  from  A  to  B  crosses  it,  than  at  any  other  point 
and  that  it  slopes  gently  both  to  the  front  and  rear, 
commanding  all  ground  within  cannon  range. 

The  natural  features  of  the  ground  are  shown  in 
the  sketch. — A  wood  W  of  considerable  size  in  front 
of  the  centre  of  the  left  of  the  position  ;  a  village 
at  B?  outside  of  cannon  range  ;  a  wood  at  D?  ^^so 
outside  oi  cannon  range  ;  a  small  collection  of  build- 
ings at  the  cross-roads  at  C ;  ^  wooded  slope  upon  the 
right  of  the  position  ;  a  farm-house,  capable  of  being 
put  in  a  defensive  condition,  almost  on  the  general  line 


HASTY  INTRENCHMENTS,  215 

to  be  occupied ;  etc,  form  the  most  prominent  features 
of  the  ground. 

Good  roads  traverse  the  country  ;  the  one  leading 
from  A  to  B?  being  a  turnpike ;  the  others,  common 
roads  such  as  are  seen  generally  in  the  country.  The 
road  from  H  to  K  has  worn  into  the  surface,  forming 
a  sunken,  or  whatr  is  generally  known  as  a  hollow 
road.  The  country  is  open  and  cultivated ;  inter- 
sected with  ordinary  farm  fences,  and  divided  into 
fields  for  pasturage,  cultivation,  etc. 

The  commander  ascertains  from  the  reconnoissance 
that  the  high  ground  at  P  must  be  held  at  all  hazards  ; 
that  this  part  of  the  line  forms  the  key  point  of  the 
position.  That  the  woods  at  W  ai-e  too  large  to  be 
^•slashed"  in  the  time  at  his  disposal.  They  must 
therefore  be  defended  and  made  so  strong  as  to  re- 
move all  danger  of  the  enemy's  obtaining  possession 
of  them. 

The  number  of  troops  forming  the  army  corps  is 
about  thirty-four  thousand,  and  is  sub-divided  into 
divisions,  brigades,  etc.  For  simplicity  of  details,  the 
corps  will  be  supposed,  in  this  example,  to  be  divided 
into  six  brigades,  of  six  regiments  each,  and  its  com- 
position to  be  as  follows  : 

Six  brigades  of  infantry,  three  regiments  of  cavalry, 
twelve  batteries  of  field  artillery,  three  batteries  of 
horse-artillery,  and  six  companies  of  engineer  troops. 
These  will  number  about  as  follows  : 


^  1 » '  FIE  1. 1)   FOU  TIFICA  TIONS, 

Thircy-six  regiments  of  infantry,  .  .  . 

Three  regiments  of  cavalry,  .  . 

Fifteen  batteries  of  artillery,  .  .  . 

Six  companies  of  engineer  troops,  .  . 

Total 


27,000  men 
3,600    " 
2,250    •• 
900    •• 

33,750    •• 


Since  the  left  of  the  line  is  to  be  the  most  strongly 
defended,  the  commander  distributes  his  infantry  as 
follows :  one  brigade  upon  the  right ;  two  brigades 
upon  the  left ;  two  brigades,  to  defend  the  ground  be- 
tween the  right  and  left,  and  the  remaining  brigade 
in  reserve. 

The  brigades  are  placed  about  as  follows :  The  first 
brigade  being  expected  to  defend  the  high  ground 
at  R,  may  be  posted  as  follows  :  two  regiments  in  the 
intrench  men  ts  .?,  .<?,  on  the  right  and  left  of  the  bat- 
tery at  1  ;  one  regiment  in  the  skirt  of  the  woods  on 
the  right,  supported  by  another  regiment  near  it 
but  hidden  by  the  slope  of  the  hill;  two  regiments 
should  be  placed  a  short  distance  in  rear  of  the  right, 
to  form  a  second  line  and  act  as  supports  to  the  first 
line.  The  second  brigade  is  placed  on  the  left  of  the 
first,  as  follows  :  three  of  its  regiments  deployed  be- 
hind the  crest  of  the  hill  ;  the  remaining  three,  the 
troops  being  in  column,  should  be  in  rear  of  the 
others,  forming  a  second  line.  The  third  brigade  is 
placed  on  the  left  of  the  second,  as  follows  :  three 
of  its  regiments  deployed   along  the  slope   upon    the 


HASTY  TNTRENCH31ENTS.  217 

same  general  line  formed  by  the  second  brigade ;  one 
regiment  placed  in  the  works  s,  s,  near  the  battery 
at  2,  as  a  support  to  the  guns  ;  the  remaining  two 
regiments  in  rear,  forming  a  second  line.  The  fourth 
and  fifth  brigades  are  to  defend  the  left.  The  whole 
of  the  fourth  brigade  is  posted  in  the  woods  VV,  three 
of  its  regiments  deployed  along  the  skirts  of  the  woods 
on  the  sides  towards  the  enemy,  and  the  remaining 
three,  in  column,  in  convenient  supporting  distances. 
The  fifth  brigade  has  one  regiment  posted  at  the 
farmhouse  ;  one,  in  the  intrenchments  s,  s,  support- 
ing the  batteries  at  3  ;  one,  supporting  the  battery 
at  4  ;  and  the  remaining  three  regiments  behind  the 
woods,  as  shown  in  the  figure.  The  sixth  brigade 
forms  a  reserve,  and  occupies  a  convenient  position  in 
rear  near  the  road  coming  from  Ai 

The  artillery  is  posted  as  follows  :  two  batteries 
upon  the  high  ground  on  the  right,  commanding  the 
approaches  in  that  direction, — marked  on  the  figure 
at  1  ;  one  battery,  in  the  interval  between  the  second 
and  third  brigades,  at  2  ;  two  batteries,  on  the 
left  of  the  third  brigade  at  3 ;  one  battery  on  the 
left  at  4 ;  one  battery,  in  the  front  edge  of  the 
wood  W  ;  two  batteries,  in  the  second  line  behind 
the  second  brigade  ;  one  battery  in  the  second  line 
behind  the  third  brigade  ;  one  battery  of  horse  artil- 
lery with  the  cavalry  on  the  right ;  and  the  remaining 
batteries,  four  in  all,  with  the  reserve. 


21S  FIELD  FORTIFICATIONS. 

The  cavalry  is  posted  as  follows  :  one  regiment 
behind  the  right  wing ;  one  behind  the  left  wing ; 
and  one  with  the  reserve.  The  cavalry  on  the  right 
may  be  divided  inta  two  parts,  one  part  is  posted 
behind  the  extreme  right,  the  other  behind  tlie  sec- 
ond brigade.  The  cavalry  behind  the  left  wing  may 
be  divided  into  two  parts,  one  is  posted  behind  and 
near  the  farmhouse,  the  other  behind  the  wood  W  and 
near  the  main  road. 

The  engineer  troops  are  distributed  along  the  en- 
tire front,  engaged  in  the  preliminaries  belonging  to 
the  work  of  intrenching  the  position.  These  prelimi- 
nary operations  consist  in  putting  the  woods  W  in 
front,  the  woods  upon  the  right,  and  the  farm-house, 
in  a  condition  of  defence  ;  in  laying  out  the  shelter 
trencheS;  a,  b,  c,  etc.,  and  posting  the  working  parties 
detailed  to  construct  them  ;  and  in  tracing  the  epaul- 
ments,  1,  2,  3  and  4,  and  the  field  works,  s,  5,  6?,  etc., 
intended  for  the  batteries  and  their  supports. 

The  woods  W  ai'^  put  in  a  state  of  defence  as  de- 
scribed in  article  179.  The  battery  posted  in  the 
edge  is  placed  so  as  to  sweep  with  its  fire  both  of 
the  roads  leading  to  the  woods.  The  batteries  at 
3  and  4  are  placed  so  as  to  cross  their  fire  upon  the 
ground  in  front  of  the  woods. 

The  woods  on  the  right  are  arranged  in  a  similar 
manner  to  afford  an  obstacle  to  the  enemy  moving  in 
that  direction. 


HASTY  INTRENCHMENTS,  219 

All  obstructions  existing  upon  the  ground  in  front 
of  the  position  which  can  be  made  to  interfere  with 
the  movements  of  the  enemy  are  preserved  and  added 
to  ;  all  those  which  would  screen  his  movements  or 
afford  him  shelter,  are  removed  or  torn  down. 

The  hollow  road  in  rear  should  have  its  banks 
cut  down  so  as  not  to  interfere  with  the  movements 
of  the  troops  in  crossing  from  one  side  to  the  other. 

The  farm-house  is  arranged  as  described  in  article 
174.  The  shelter  trenches  and  the  epaulments  for 
the  batteries  are  constructed  as  previously  described. 

The  field  works,  s,  s,  .9,  etc.,  have  the  traces  of 
blunted  redans,  or  of  lunettes  with  obtuse  salients. 
The  faces  should  be  made  from  seventy  to  eighty 
yards  long,  and  so  directed  as  to  sweep  the  slopes  in 
front.  It  is  recommended  to  place  in  each  work,  a  re- 
dan-shaped, defensive  traverse  arranged  as  indicated  in 
the  figure,  and  to  give  it  a  command  equal  to  or 
greater  than  the  parapet  of  the  work. 

These  works  should  be  placed,  so  as  to  leave  an 
interval  of  not  less  than  one  hundred  yards,  between 
their  flanks  and  the  batteries  they  support. 

The  profile  of  these  works,  s,  s,  etc.,  should  ap- 
proximate as  nearly  as  possible  to  the  normal  profile. 
The  time  disposable  for  their  construction  will  de- 
cide upon  the  command  they  shall  have.  By  placing 
working  parties  upon  both  sides  of  the  parapet,  con- 
structing the  part   in  rear  of  the  interior  crest  with 


220  FIELD   FORTIFICATIONS. 

the  profile  shown  in  Figs.  81  and  82,  and  construct- 
ing the  part  in  front  with  the  normal  profile,  a  strong 
work  can  be  quickly  built. 

It  will  be  seen,  that  the  commanding  general,  by 
the  use  of  these  intrenchments  thus  hastily  constructed, 
can  concentrate,  without  risk,  the  greater  part  of  his 
corps  upon  the  left,  the  key  point  of  his  position.  By 
their  use,  he  is  able  to  supply  the  want  of  numbers 
and  thus  strengthen  his  line.  The  principles  observed 
in  this  example  apply  equally  to  a  position  of  greater 
or  less  extent. 


CHAPTER    XV. 

ATTACK   AKB   DEFENCE   OF   FIELD   FORTIFICATIOKS. 

182.  Attack. — An  attack  made  to  capture  a 
field  work,  or  to  carry  a  line,  may  be  a  quick^  sud- 
den effort,  or  it  may  be  a  prolonged  one.  The  for- 
mer is  known  as  an  assault*  the  latter,  a  siege. 

Assaults  are  of  two  kinds ;  open  assaults  and  those 
made  with  great  secrecy. 

Whatever  be  tlie  kind  of  assault,  it  should  be  pre- 
ceded by  reconnoissances,  made  as  full  as  possible, 
for  the  purpose  of  ascertaining  the  best  and  easiest 
approaches  to  the  work,  the  nature  and  position  of 
the  obstacles,  the  numbers  and  kinds  of  troops  com- 
posing the  garrison,  and  the  strength  and  positions 
of  the  reserves,  exterior  to  the  work,  but  near  enough 
to  take  part  in  its  defence. 

Particular  attention  should  also  be  paid  to  the  po- 
sitions for  the  artillery  of  the  attack.  These  posi- 
tions should  be  such  that  the  guns  can  bring  enfilading 
fires,  on  the  principal  faces  of  the  work,  strong  cross 
fires  upon  the  point  of  attack,  and  if  possible,  a 
sweeping  fire  on  the  approaches  to  the  work  in  rear. 
An  important   point,  to  be  observed    in  this  matter,  is 


232  FIELD  FORTIFICATIONS. 

to  select,  if  possible,  positions  from    which    the   guns 
will  not  have   to  be  removed  during  the  attack. 

183.  Open  assault.— An  assault  of  this  class 
is  made  suddenly,  and  if  possible,  without  the  enemy's 
knowing  it  until  the  rush  is  made.  It  is  an  open 
assault,  because  the  approach  is  made  openly,  though 
the  attack  be  unexpected. 

The  assault  may  be  divided  into  three  periods,  as 
follows  : 

1.  The  preliminary  operations,  and  the  artillery 
attack. 

2.  The  advance  of  the  attacking  troops  from  the 
cessation  of  the  cannonade,  until  they  arrive  at  the 
counterscarp  of  the  ditch. 

3.  The  assault  of  the  parapet,  and  the  capture  of 
the  work. 

184.  The  preliminary  operations  consist  in  se- 
lecting the  points  of  attack  ;  designating  the  troops 
to  make  the  attack,  and  placing  them  in  position  ; 
organizing  bodies  of  pioneers,  or  engineer  troops  to 
remove  obstacles ;  and,  etc.  It  is  supposed  that  the 
outposts  of  the  enemy  are  all  driven  in,  and  his  troops 
are  within  the  work,  or  under  its  immediate  protec- 
tion. 

A  heavy,  converging  fire  of  artillery,  within  accu- 
rate range,  has  been  deemed  by  military  authorities 
to  be  an  essential  element  of  success  in  an  open  as- 
sault.    The  manuals  all  prescribe,  in  an  open  assault, 


ATTACK  Ayn  DEFENCE  OF  FIELD  FORTIFICATIONS.  223 

an    artillery  attack    preceding  the  forward   movement 
of  the  attacking  forces. 

The  objects  expected  to  be  attained,  by  this  artil- 
lery fire,  are  as  follows  : 

1.  To  silence  the  artillery  of  the  defence. 

2.  To  damage,  and   possibly  to  destroy  the  works. 

3.  To  inflict  losses,  and  to  harass  the  men  to  such 
an  extent,  that  they  may  become  demoralized. 

The  first  object  is  attainable.  The  theory  of  an 
open  assault  supposes  a  superiority  of  members  upon 
the  part  of  the  attacking  forces,  and  a  superiority  of 
artillery.  When  this  is  the  case,  the  silencing  of  the 
artillery  of  the  defence  becomes  a  mere  matter  of  time. 

The  second  object  is  hardly  practicable  so  far  as 
its  destruction  is  concerned,  if  the  work  is  made  of 
earth,  and  has  a  good  profile.  The  fire  may,  however, 
be  successful  in  tearing  up  the  superior  slope,  destroy- 
ing the  improvised  loop-holes,  and  producing  irregalari- 
ties  in  the  interior  crest  of  the  parapet.  The  amount 
of  damage  which  can  be  made,  will  depend  upon  the 
amount  of  fire  that  can  be  concentrated  upon  the 
work.  The  effect  of  the  damage  will  be  to  impair,  more 
or  less,  the  confidence  of  the  men,  in  the  efficacy  of 
the  work  to  shelter  them. 

The  third  object  may,  or  may  ndt  be,  attained. 
The  kind  of  shelters,  the  strength  of  the  parapet,  and 
the  character  of  the  troops  are  factors  of  the  problem. 

The    conclusions    drawn    from    recent  experiences 


224  FIELD  FORTIFICATIONS, 

are,  that  an  attack  by  artillery,  preliminary  to  an  open 
assault,  may  be  useful  against  works  of  weak  profiles 
not  provided  with  bomb-proofs,  but  against  strong 
works  with  good  interior  arrangements,  the  artillery 
attack  is  of  little  service,  and  may  be  injurious  to  the 
attack  so  far  as  it  serves  the  defence  as  a  warning  of 
the  proposed  assault. 

185.  The  features  of  the  second  period  are  the 
advance  of  the  attacking  forces,  and  their  progress  to 
the  ditch.  The  advance  is  made  by  a  line  of  infantry, 
in  extended  order,  preceded  by  skirmishers.  A  second, 
and  even  a  third  line,  follows  the  first. 

The  skirmishers  advance  by  '^  rushes,''  taking  ad- 
vantage of  every  inequality  in  the  surface  to  shelter 
themselves,  and  being  reinforced  continually  from  the 
line  in  their  rear.  Accompanying  the  line  of  supports 
are  pioneers,  or  engineer  troops,  provided  with  tools, 
etc,  to  remove  or  to  make  passages  through  all  ob- 
stacles in  the  way  of  the  approach.  The  skirmishers 
keep  up  a  sharp  fire  upon  the  parapet,  while  the 
obstacles  are  being  removed,  and  while  the  supports 
are  forming  in   the  ditch,  or  on  the  berm. 

The  methods  of  removing  these  obstacles  are  de- 
scribed in  the  books,  and  manuals,  relating  to  practical 
engineering  operations. 

186.  The  third  period  includes  the  assault  upon 
the  parapet  and  all  succeeding  operations. 

As  soon  as  a  sufficient  number  of  the  troops  have 


ATTACK  AND  DEFENCE  OF  FIELD  FORTIFICATIONS.  225 

assembled  in  the  ditch,  or  upon  the  berm  of  the  work, 
the  assault  upon  the  parapet  is  made  by  a  rush  of  these 
troops  in  a  body  up  the  exterior  slope  and  over  the 
the"  parapet  into  the  work. 

If  a  defence  is  still  continued,  a  hand-to-hand  con- 
flict follows.  This  should  result  in  a  capture  of  the 
work  in  consequence  of  the  superiority  of  numbers  on 
the  part  of  the  assailants. 

If  the  defenders  should  have  left  the  parapet  upon 
the  assailants  reaching  the  ditch,  it  may  be  that  they 
have  done  so  for  the  purpose  of  occupying  some  in- 
terior retrenchment,  or  block-house.  In  this  case,  the 
guns  of  the  work,  if  any,  should  be  turned  against  the 
retreating  forces  and  steps  be  taken  to  attack  the  inner 
defences.  An  examination  of  the  powder  magazines 
should  be  made  immediately,  to  guard  against  explo- 
sions either  accidental  or  intentional. 

Steps  should  be  taken,  as  soon  as  the  work  is  cap- 
tured, to  put  it  in  a  state  of  defence  against  recap- 
ture, if  it  is  to  be  occupied,  or  to  destroy  it,  if  it  is  to 
be  abandoned, 

187.  An  attack  made  secretly. — The  pre- 
liminaries of  a  secret  attack  are  identical  with  those  of 
an  open  assault,  except  in  the  secrecy  of  the  move- 
ments which  are  made.  The  troops,  who  are  to 
make  the  attack,  are  kept  in  ignorance  of  the  object 
of  their  movements  until  they  are  assembled  at  the 
point  from  which  they  are  to  make  the  attack. 


22G  FIELD   FORTIFICATIOXS, 

The  success  of  the  attack  depends  upon  its  being 
unexpected  by  the  defence,  and  upon  finding  the 
defenders,  in  a  measure,  unprepared  to  resist  it.  An 
attack  of  this  kind  is  a  surprise,  and  is  known  fre- 
quently as  an  attack  by  surprise. 

188.  Success  in  either  case,  an  attack  made 
openly  or  secretly,  is  greatly  dependent  upon  finding 
the  enemy  unprepared  to  resist  the  assault.  The  attack 
should  therefore  be  made  suddenly,  and  without  the 
enemy  suspecting  the  intention. 

189.  Attack  by  artillery  only. — Under  the 
circumstance  that  the  attacking  forces  are  overwhelm- 
ingly superior  in  artillery,  it  is  possible,  in  works  hastily 
constructed  and  not  properly  provided  with  interior 
defences,  to  force  a  garrison  to  capitulate  by  use  of 
artillery  alone,  supplemented  by  sharp-shooters  who 
may  be  able  to  get  near  enough  to  the  works  to  pick 
off  the  gunners  of  the  work. 

190.  Key-point. —Great  care  must  be  taken  to 
direct  the  assault  upon  the  key-point  of  the  in- 
trenched line  or  position.  The  mistake  has  been  fre- 
quently make  of  directing  the  main  attack  upon  the 
wrong  point,  which  attack  when  successful,  produced 
no  lasting  benefit  to  the  victorious    troops. 

191.  Defence. — Fortifications  are  inert  masses, 
passive  in  their  nature,  which  become  obstacles  to  an 
enemy's  approach  only  when  fully  manned  by  well- 
armed,  courageous  and  vigilant  troops. 


ATTACK  AND  DEFENCE  OF  FIELD  FORTIFICATIONS.  227 

A  field  work  performs  all  that  is  required  of  it, 
when  it  compels  a  force,  superior  in  number  to  its 
garrison,  to  resort  to  the  tedious  and  costly  operations 
of  a  siege  to  take  it ;  or  makes  this  force  move  in  an- 
other direction  to  gain  its  ends. 

The  military  man  should  remember  that  a  well- 
arranged  intrenchment,  or  field  work,  should  obstruct 
the  enemy's  approach,  as  well  as  give  shelter  to  its  de- 
fenders. It  is  a  question,  oftentimes,  difficult  to  an- 
swer, as  to  which  of  the  two,  the  shelter  to  the  defence, 
or  the  obstruction  of  the  enemy,  is  the  more  import- 
ant. Either  one  gives  an  increase  of  resistance  to  the 
defence,  and  the  two  combined  form  an  obstacle  diffi- 
cult to  surmount. 

An  enemy  may  succeed  by  brute  force  and  sheer 
numbers,  in  carrying  a  position  in  which  the  defend- 
ers are  sheltered  simply,  or  a  position  arranged  with 
obstacles  that  hold  him  under  fire  at  close  range  ; 
but  the  success  is  accompanied  by  such  heavy  losses, 
that  the  victory,  in  many  cases,  had  better  be  classed 
as  a  defeat.  This  is  particularly  so,  where  the  two 
are  combined. 

It  is  well  to  be  remembered,  that  a  vigorous  de- 
fence .requires  that  every  part  of  a  field  work,  or  line, 
should  be  guarded  by  a  sufficient  number  of  troops  to 
repel  any  assault  that  an  enemy  might  make,  and 
that  numbers  alone  are  not  sufficient.  Endurance, 
courage,  and  vigilance  are  necessary  in  the  commander 


2^S  FIELD   FORTIFICATIONS. 

and  his  troops.  No  better  motto  can  be  devised  for 
the  banner  of  the  defence,  than  the  trite  aphorism  so 
frequently  quoted, 

**  Eternal  vigilance  is  the  price  of  liberty." 

The  memoranda,  compiled  for  the  use  of  the  offi- 
cers, commanding  the  different  field  works,  surrounding 
the  City  of  Washington,  during  the  war  of  1861-5,  may 
be  quoted  in  this  connection.  The  precautions  therein 
recommended  to  be  taken,  and  the  course  advised  for 
each  commanding  officer,  are  given  in  detail  and  arc 
as  applicable    in  the  future  as  they  were  in  the  past. 

192.  Memoranda  compiled  for  the  guid- 
ance and  information  of  officers  serving  in  the  de- 
fences of  Washington. 

••'•  1.  The  number  of  men  required  for  the  garrison 
of  each  work  (artillery  and  infantry  supports  in- 
cluded) has  been  calculated,  and  should  be  known  to 
every  commanding  officer  of  a  fort ;  but  it  will  be  for 
the  brigade  and  division  commanders,  or  for  the  com- 
manding general,  to  determine  the  necessity  of  filling 
up  each  garrison  to  its  full  siege  complement  and  of 
manning  the  connecting  lines  of  rifle-trenches. 

^•2.  It  is  the  duty  of  a  commanding  officer  of  a 
fort  to  see  that  he  has  all  the  means  and  appliances 
that  may  be  wanted  during  a  siege  provided  before- 
hand. If  his  position  be  somewhat  isolated  and 
where  the  enemv  mav  cut  off  his  communications,  he 


ATTACK  AXD  DEFENCE  OF  FIELD  FORTIFICATIONS,  229 

should  see  that  he  has  an  ample  supply  of  provisions 
stored,  either  in  his  fort,  or  in  a  secure  place  in  its 
rear ;  and  he  must  take  measures  to  keep  an  abun- 
dant supply  of  water  in  the  fort,  both  for  the  use  of 
the  garrison  and  to  extinguish  fires. 

'•  He  should  see  that  his  fort  is  provided  with  all 
the  tools  that  may  be  wanted  during  the  siege,  par- 
ticularly with  shovels,  picks,  axes,  saws,  augers, 
and  hammers.  Further,  he  should  provide,  either  be- 
forehand or  as  soon  as  possible  after  the  siege  com- 
mences, all  the  materials  that  may  be  wanted  during 
the  siege,  such  as  an  abundant  supply  of  timber,  of 
plank,  of  nails,  spikes,  of  sand  bags,  gabions,  and 
fascines.  Timber  is  of  the  first  importance  ;  a  large 
supply  of  it  should  therefore  be  secured. 

^'  3.  When  any  ]3art  of  the  line  of  defence  is  threat- 
ened with  an  attack,  all  houses,  trees,  bushes,  and  in 
general  everything  that  could  be  used  as  a  cover  by 
the  enemy's  sharpshooters,  should  be  at  once  removed 
for  a  distance  of  at  least  six  hundred  yards  from  the 
line.  If  sharpshooters  can  be  concealed  within  that 
distance  of  a  fort  or  battery,  they  will  pick  off  the 
cannoniers  and  the  guns  cannot  be  served  without 
serious  loss. 

''  In  conducting  the  defence  of  a  fort,  each  company 
or  detachment,  should  have  its  particular  post  and 
duty  assigned  to  it,  and  receive  special  instructions 
as  to  their  duties  in  all  possible  contingencies. 


^30  FIELD   FORTIFICATIONS, 

"  Commanding  officers  should  be  careful  to  see  that 
uU  their  subordinates  thoroughly  understand  the 
ground;  both  in  his  front  and  rear,  and  are  familiar 
with  all  the  roads  and  paths ;  they  should  know  by 
a  careful  examination  of  the  ground  in  front  the 
points  which  an  enemy  would  select  for  batteries, 
and  the  exact  ranges  to  such  points,  and  should  study 
out  how  best  to  arrange  their  own  guns  to  contend 
with  such  batteries  should  they  be  erected ;  tlioy 
should  know  the  relations  of  the  fort  they  occupy  to 
the  adjacent  works,  and  be  familiar  with  all  the  re- 
sources that  may  be  made  available  daring  the  de- 
fence. This  information  should  be  imparted  by  them 
to  the  non-commissioned  officers,  and  in  some  cases 
to  the  privates ;  for  it  should  be  remembered  that 
the  fate  of  the  fort  may  depend  upon  the  good  or  bad 
conduct  of  one  individual. 

*'  There  should  be  a  reserve  in  all  cases.  It  should 
be  posted  in  the  bomb-proofs,  or  behind  traverses  and 
magazines,  or  under  temporary  shelter  made  by  lean- 
ing timber  against  parapets,  magazines  and  bomb- 
proofs,  or  by  digging  trenches  in  the  ground  and 
covering  them  with  timber  and  earth. 

*'  Strict  vigilance  should  be  exerted  to  guard  against 
surprise  ;  for  this  purpose,  when  the  enemy  approaches, 
a  chain  of  sentinels  should  be  posted  in  front  of  the 
works,  and  as  far  to  the  front  as  practicable,  taking 
particular    care   to    have    them    posted   at    all    points 


ATTACK  AND  DEFENCE  OF  FIELD  FORTIFTCATIONS.  231 

where  an  enemy  might  approach  the  works  without 
being  seen,  either  for  the  purpose  of  reconnoitering 
or  delivering  an  assault;  but  the  general  arrangement 
of  sentinels  must  be  made  by  brigade  or  division  com- 
manders. 

''  By  keeping  up,  both  by  day  and  night,  such  a 
chain  of  sentinels  in  front  of  the  works,  and  by  post- 
ing, where  practicable,  a  few  sharpshooters  in  holes 
or  rifle-pits  in  front  of  each  fort,  the  efforts  of  tlie 
enemy  to  obtain  the  information  he  wants  before 
commencing  the  siege  batteries  will  be  greatly  re- 
tarded, and  time  afforded  to  the  defender  for  com- 
pleting the  preparations  to  receive  him. 

"If  the  sentinels  are  driven  in  and  an  attack  is  ap- 
prehended at  night,  fire  and  light  balls  should  occa- 
sionally be  fired  to  the  front,  taking  care,  however, 
not  to  set  fire  to  the  abatis ;  and  in  this  case  the 
guns  should  be  double-shotted,  and  pointed  if  possi- 
ble, by  daylight,  so  as  best  to  sweep  the  ground  with- 
in a  distance  of  six  hundred  yards,  depending  on  the 
configuration  of  the  surface  in  each  particular  case. 

"If  the  ditches  are  not  flanked  shells  loaded  with 
service  charges  and  ten-second  fuzes,  should  be  placed 
on  the  banquettes  in  charge  of  men  specially  instructed 
how  to  use  them.  These  men  should  be  provided  with 
pieces  of  burning  slow-match. 

"Hand  grenades,  loaded  and  capped,  should  also  be 
placed  ready  for  use,  and,  finally,  the  men  should  sleep 


23;^  FIELD    FORTIFICATIONS, 

at  their  guns  and  every  man  should  know  his  post 
and  his  duty.  Shells  and  also  hand  grenades  may  be 
exploded  by  attaching  a  string  in  such  a  way  that  the 
act  of  rolling  them  or  throwing  them  will,  as  soon  as 
the  string  is  brouglit  taut,  explode  a  percussion  cap 
or  friction  tube. 

"  4.  If  the  enemy  should  open  his  attack  by  a  warm 
cannonade,  and  concentrate  his  fire  upon  a  particular 
fort,  the  troops  should  not  be  unnecessarily  exposed 
to  it,  if  they  can  be  siieltered  near  the  posts  they  are 
to  occupy  when  an  assault  is  made.  If  the  cannon^ 
ade  should  become  too  warm  for  the  garrison  to  reply 
without  too  much  loss,  the  field  and  siege  guns  should 
be  removed  from  their  embrasures  and  placed  behind 
the  parapets  or,  in  case  of  an  enfilading  fire,  behind 
traverses,  bomb-proofs,  etc. 

"  During  a  cannonade  the  dead  and  seriously  wound- 
ed should  be  kept  out  of  sight. 

^'  When  the  assault  is  made,  this  cannonade  of  the 
enemy  must  cease  in  order  not  to  injure  his  own  troops. 
The  guns  are  then  run  into  position  and  every  man 
resumes  his  post.  The  men  should  be  instructed  to 
reserve  their  fire  until  the  enemy  has  arrived  at  cer- 
tain points,  marked  out  in  front  of  the  works,  where 
it  will  be  most  effective. 

"  Particular  attention  should  be  given  to  securing  the 
gate-way.  The  abatis  in  front  should  be  made  con- 
tinuous.    As  the  gates  are  made  to  open  inward,  the 


ATTACK  AND  DEFENCE  OF  FIELD  FORTIFICATIONS.  233 

enemy  cannot  easily  open  them  outward.  The  danger 
^0  fear  is  that  he  will  force  them  inward,  or  lift  them 
off  their  hinges.  To  prevent  the  first,  roll  a  heavy  log 
against  the  inside  of  the  gate,  plant  posts  or  drive 
strong  stakes  behind  it,  and,  for  greater  security,  cover 
the  log  with  earth.  The  second  danger  may  be  pre- 
vented by  ''upsetting"  the  head  of  the  pintle  upon 
which  the  gate  turns,  or  still  easier  by  driving  a  strong 
spike  immediately  over  it.  If  the  gate- way  is  not 
flanked  it  may  be  necessary,  in  some  cases,  to  increase 
the  dirt  over  the  log  until  it  becomes  an  infantry  para- 
pet. Communication  with  the  interior  may  be  kept 
up  by  one  or  more  light  movable  bridges,  made  of 
plank  or  boards,  leading  from  the  parapet  across  the 
ditch.  These  bridges  should  be  kept  inside  the  fort 
at  night,  or  when  an  attack  is  anticipated. 

''  5.  Every  precaution  should  be  taken  to  secure  the 
magazines  against  vertical  or  curved  fire.  The  en- 
trance is  the  weak  point  ;  hence,  where  necessary, 
cover  it  by  additional  earth  ;  put  sphnter-proof  guards, 
made  of  timber  or  plank,  around  the  door,  and  have 
water  at  hand,  in  barrels  or  casks,  to  extinguish  any 
fire  near  the  doorway  ;  keep  both  doors  shut,  especially 
the  inner  one,  allowing  only  one  or  two  men  to  be 
inside,  and  only  the  ordnance  sergeant,  with  an 
ussistant,  on  the  stairway  to  pass  out  tlie  ammunition 
that  may  be  called  for.  Keep  all  the  ventilators 
closed,    and   fill   as  far   as  practicable,    all  ventilating 


234:  FIKLr>    FORTIFICATIOXS. 

tubes  with  earth  both  outside  and  inside  of  the 
magazines. 

*'  See  that  an  ample  supply  of  wads  is  kept  x>n  hand 
outside  of  the  magazines,  and  that  the  ordnance  ser- 
geant makes  careful  report  of  the  ammunition  ex- 
pended, and.  that  it  is  promptly  replaced. 

"Fill  at  once  any  holes  made  in  the  magazine  cover. 
Logs,  fascines,  or  even  sticks,  laid  against  its  exposed 
side,  greatly  reduce  the  penetration  of  shot,  particu- 
larly of  elongated  projectiles,  by  deflecting  them. 

**  6.  Build  merlons  between  barbette  guns,  and  par- 
tially till  wide  embrasures,  as  soon  as  the  positions  of 
the  enemy's  batteries  and  the  proper  direction  of  fire  of 
each  gun  are  ascertained.  Cut  away  the  foot  of  scarps 
to  render  escalade  more  difficult,  taking  care  not  to 
endanger  the  stability  of  the  parapet.  Use  earth  so 
obtained  for  making  a  glacis  and  traverses  across  the 
abatis,  if  it  be  threatened  by  an  enfilading  fire.  A 
few  piles  of  earth  across  the  abatis,  particularly  if  the 
earth  be  wet,  is  a  great  security  against  such  fire. 

''  Commanding  officers  of  the  forts  cannot  be  too 
strongly  impressed  with  the  fact  that  the  abatis  is 
one  of  the  main  sources  of  strength  to  a  field  work. 
It  should  be  carefully  protected  from  injury  and  dep- 
redation, fire,  etc. 

"  7.  Bury  percussion  shells  or  hand  grenades,  to  act 
as  torpedoes,  in  the  bottom  of  the  ditch  and  outside 
of  the  abatis. 


ATTACK  AND  DEFENCE  OF  FIELD  FORTIFICATIONS,  235 

'^8.  Put  up  traverses  on  all  faces  liable  to  be  eu- 
filaded,  to  protect  the  guns,  even  if  to  obtain  room  for 
them  some  of  the  guns  have  to  be  removed  ;  repair 
all  damages  to  the  parapet,  on  the  following  night,  if 
not  practicable  to  do  it  before. 

"Earth  may  be  obtained  for  the  above  nses  by  ex- 
cavating in  the  terreplein  for  bomb-proof  shelters,  and 
by  digging  pits  or  holes,  about  three  feet  wide  and 
deep,  where  ricochet  shells  are  most  likely  to  fall, 
and  where  the  excavations  will  not  seriously  interfere 
with  the  defence  ;  remove  all  sheds  and  wooden 
buildings  lest  they  take  fire. 

'•9.  Construct  temporary  banquettes  on  all  bomb- 
proofs  and  magazines,  to  aiford  an  infantry  fire  on 
the  probable  front  or  points  of  attack.  These  may 
be  made  with  plank  resting  on  trestles  or  posts,  or 
by  cutting  away  the  earth  so  as  to  afford  standing 
room  for  infantry,  with  a  parapet  in  front. 

*'  10.  When,  or  before,  the  ^enemy's  approaches  have 
been  advanced  to  the  vicinity  of  the  work,  a  surprise, 
or  sudden  assault  upon  one  or  more  of  the  forts,  es- 
pecially by  nighfc,  may  be  anticipated.  Under  such 
circumstances  it  is  the  duty  of  the  commanding  offi- 
cer, though  he  may  have  resorted  to  every  expedient 
to  retard  the  siege,  to  impress  upon  the  garrison  that 
they  cannot,  without  loss  of  honor,  either  abandon 
the  fort  or  surrender  it  without  resisting  at  least  one 
assault.      Such   is   the   inexorable   law   of   war,  and  it 


230  FfKH)    FOimF/CATIONS. 

should  not  be  forgotten  that  it  holds  good  wlietlier 
or  not  there  are  other  works  in  the  rear  to  which 
the  garrison  miglit  retire  with  comparative  safety. 
When  the  attack  is  about  .to  be  made,  the  command- 
ing officer  of  a  fort  should  endeavor  to  inspire  his 
men  with  confidence  in  their  powers  of  resistance, 
with  self-reliance  and  enthusiasm. 

"  Every  preparation  should  be  made  to  resist  the 
passage  of  the  ditch,  by  the  fire  of  artillery  and  in- 
fantry, by  torpedoes,  by  loaded  shell  and  hand-gre- 
nades, and  by  attacking  the  enemy  on  the  parapet. 

''  The  commanding  officer  must  decide  beforehand, 
according  to  the  particular  circumstances  under  which 
he  is  called  upon  to  act,  how  this  attack  should  be 
made.  If  there  be,  behind  bomb-proofs  and  maga- 
zine, banquettes  and  breast-heights  for  infantry  bear- 
ing on  the  points  of  attack,  then,  at  the  proper  mo- 
ment, the  field-pieces  and  howitzers  should  be  with- 
drawn from  the  platforms,  loaded  with  double  charges 
of  canister  and  placed  in  positions  where  they  may 
still  be  used  against  the  enemy  as  he  appears  on  the 
crest  of  the  parapet  or  descends  to  the  terreplein  ; 
while  the  infantry  should  line  these  interior  parapets 
and  aid,  by  their  fire,  in  driving  the  enemy  from  the 
work,  the  reserve  charging  furiously  with  the  bayonet 
on  the  appearance  of  any  confusion  or  disorder. 

^•'If  there  be  no  such  interior  lines  of  infantry  fire 
on  the  point  of  attack,   then  the  enemy  must  he  met 


ATTACK  AND  DEFENCE  OF  FIELD  FORTIFICATIONS,  237 

with  the  bayonet  on  the  top  of  the  parapet.  For 
this  pui-pose  one  or  more  steps,  made  of  boards, 
should  be  prepared  beforehand,  to  enable  the  infantry 
to  mount  the  parapet,  and  it  should  be  impressed  on 
the  defenders  that  the  assaulting  troops,  arrived  at 
position,  will  be  greatly  fatigued,  and  necessarily  in 
disorder,  and,  moreover,  will  be  cut  off  from  all  ex- 
ternal support,  and  hence  that  it  is  an  opportune 
moment  by  a  vigorous  assault  with  the  bayonet  to 
hurl  the  enemy  into  the  ditch  and  to  retrieve,  with 
disaster  to  the  foe,  the  endangered  possession  of  the 
work  and  of  the  defensive  line  on  which  the  safety 
of  the  nation  depends. 

''  The  firing  of  the  guns,  particularly  howitzer  and 
field-pieces,  loaded  with  canister,  should  be  continued 
as  long  as  possible  in  order  to  delay  the  advance  of 
the  supporting  columns  ;  and,  if  the  assault  fail  and 
the  support  be  driven  back  in  disorder,  a  sortie  in 
force  may  be  made  and  the  enemy  pursued  into  his 
works. 

'•'Such  sorties,  however,  should  not  be  attempted 
by  the  troops  in  any  particular  fort,  but  should  be 
made,  under  the  direction  of  the  commanding  gen- 
eral, by  the  outside  reserves,  supported  by  the  fire 
of  all  the  forts  and  batteries  bearing  on  the  position 
to  be  taken." 

193.  Examples. — The  most  noted  examples  in  re- 
cent wars,  of  intrenched  positions,  in  which  the  works 


23cS  FIELD   FORTIFICATIONS, 

used  were  field  fortifications,  and  which  ilhistrate  the 
attack  and  defence,  are  found  in  the  cases  of  Sebastopol 
in  18o4,Vicksburg  and  Port  Hudson  in  1863.  Richmond 
and  Petersburg  in  1864,  Plevna,  in  1877-8,  etc.  The 
student  is  referred  to  these  particular  examples  for  the 
details  which  cannot  be  given  here. 

From  the  many  examples,  reference  will  be  made  here 
only  to  the  assault  made  upon  Fort  Sanders  in  1863. 

After  the  battle  of  Chickamauga,  General  Long- 
street  was  sent  into  East  Tennessee  to  capture  Knox- 
ville,  then  occupied  by  the  United  States  forces  com- 
manded by  General  Burnside.  The  latter  succeeded 
in  intrenching  his  position,  and  held  the  Confederate 
troops  at  bay. 

After  the  victory  at  Chattanooga,  General  Grant 
sent  troops  to  relieve  General  Burnside,  and  General 
Longstreet  knowing  of  their  approach  determined  to 
risk  an  assault  upon  Burnside's  position. 

He  selected  the  key  point  of  the  position,  as  the 
point  of  attack,  which  was  defended  by  an  unfinished 
earth  work,  laid  out  under  the  direction  of  Captain 
Poe  of  the  United  States  Engineers. 

There  had  not  been  time  to  make  an  abatis,  to 
build  powder  magazines,  or  even  to  revet  the  work  as 
it  should  have  been.  A  wire  entanglement  had  been 
arranged  in  front  of  the  work,  fastened  to  the  stumps 
of  the  trees  that  had  been  cut  down  to  clear  away 
the  ground. 


ATTACK  AND  DEFENCE  OF  FIELD  FORTIFICATIONS.   239 

At  dark,  on  the  28th  of  Nov.  1863,  the  Confeder- 
ate sharp-shooters  were  pushed  forward  to  within  rifle 
range  of  the  line.  At  half  past  six  in  the  morning 
of  the  29th,  a  heavy  fire  of  artillery  was  opened  on 
the  fort  and  lasted  for  twenty  minntes,  or  half  an 
hour. 

This  fire  ceased,  being  replaced  by  a  fire  of  mus- 
ketry, and  a  rush  of  a  brigade  of  infantry  upon  the 
salient  of  the  work. 

The  wire  entanglement  tripped  many  of  the  assail- 
ants^ who  fell  upon  the  ground,  but  numbers  of  them 
succeeded  in  entering  the  ditch  and  attempted  to  as- 
sault the  parapet.  The  heavy  fire  of  the  defence 
from  the  flanks  and  from  the  parapet,  drove  them 
back  and,  the  assault  failed.  General  Longstreet  then 
withdrew  his  forces. 

The  readiness,  with  which  the  assault  was  met, 
prevented  its  success. 

194.  The  history  of  attacks  made  upon  field  works 
in  recent  wars,  shows  that  assaults  upon  them  were 
generally  unsuccessful,  where  a  vigorous  defence  was 
made  ;  and  when  successful  they  were  accompanied  with 
great  loss  of  life,  and  injury  to  the  assailant. 

The  conclusion  may  be  fairly  drawn  that  a  field 
work,  vigorously  defended,  cannot  be  captured  by  as- 
sault if  it  has  a  good  profile  and  is  provided  with  the 
accessory  means  of  defence  ;  or  if  it  is  commanded  by 
other   works   which  can   not   be  assaulted  ;  or,   if  the 


240  FIELD   FORTIFICATIONS. 

garrison  can  be  readily  reinforced  from  a  strong  body 
of  troops  within  supjiorting  distance. 

A  vigorous  defence  supposes  vigilance  and  secu- 
rity against  surprise.  An  attack  may  be,  neverthe- 
less, an  unexpected  one.  and  may  task  all  the  efforts  of 
the  defence  to  repel  it.  The  success  of  an  assault  is 
greatly  dependent  upon  the  suddenness  with  which  it 
is  made,  and  a  commander  should  remember, 

"  When  'tis  done,  then  'twere  well 
It  were  done  quickly." 


OF  THK 

UNIVERSITY  ^ 


5^485 


